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December 16, 2024

Breaking Down Nation State Attacks on Supply Chains

Explore how nation-state supply chain attacks like 3CX, NotPetya, and SolarWinds exploited trusted providers to cause global disruption, highlighting the urgent need for robust security measures.
Inside the SOC
Darktrace cyber analysts are world-class experts in threat intelligence, threat hunting and incident response, and provide 24/7 SOC support to thousands of Darktrace customers around the globe. Inside the SOC is exclusively authored by these experts, providing analysis of cyber incidents and threat trends, based on real-world experience in the field.
Written by
Benjamin Druttman
Cyber Security AI Technical Instructor
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16
Dec 2024

Introduction: Nation state attacks on supply chains

In recent years, supply chain attacks have surged in both frequency and sophistication, evolving into one of the most severe threats to organizations across almost every industry. By exploiting third-party vendors and service providers, these attacks can inflict widespread disruption with a single breach. They have become a go-to choice for nation state actors and show no signs of slowing down. According to Gartner, the costs from these attacks will skyrocket “from $46 billion in 2023 to $138 billion by 2031” [1].  

But why are supply chains specifically such an irresistible target for threat actors? Dwight D. Eisenhower, the General of the US Army in World War II and former US President, once said, “you won’t find it difficult to prove that battles, campaigns, and even wars have been won or lost primarily because of logistics.”

The same is true in cyberspace and cyberwarfare. We live in an increasingly interconnected world. The provision of almost every service integral to our daily lives relies on a complex web of interdependent third parties.  

Naturally, threat actors gravitate towards these service providers. By compromising just one of them, they can spread through supply chains downstream to other organizations and raise the odds of winning their battle, campaign, or war.  

software supply chain sequence
Figure 1: Software supply chain attack cycle

A house built on open-source sand

Software developers face immense pressure to produce functional code quickly, often under tight deadlines. Adding to this challenge is the need to comply with stringent security requirements set by their DevSecOps counterparts, who aim to ensure that code is safe from vulnerabilities.  

Open-source repositories alleviate some of this pressure by providing pre-built packages of code and fully functioning tools that developers can freely access and integrate. These highly accessible resources enhance productivity and boost innovation. As a result, they have a huge, diverse user base spanning industries and geographies. However, given their extensive adoption, any security lapse can result in widespread compromise across businesses.

Cautionary tales for open-source dependencies

This is exactly what happened in December 2021 when a remote code execution vulnerability was discovered in Log4J’s software. In simple terms, it exposed an alarmingly straightforward way for attackers to take control of any system using Log4J.  

The scope for potential attack was unprecedented. Some estimates say up to 3 billion devices were affected worldwide, in what was quickly labelled the “single biggest, most critical vulnerability of the last decade” [2].

What ensued was a race between opportunistic nefarious actors and panicked security professionals. The astronomical number of vulnerable devices laid expansive groundwork for attackers, who quickly began probing potentially exploitable systems. 48% of corporate networks globally were scanned for the vulnerability, while security teams scrambled to apply the remediating patch [3].

The vulnerability attracted nation states like a moth to a flame, who, unsurprisingly, beat many security teams to it. According to the FBI and the US Cybersecurity and Infrastructure Agency (CISA), Iranian government-sponsored threat groups were found using the Log4J vulnerability to install cryptomining software, credential stealers and Ngrok reverse proxies onto no less than US Federal networks [4].  

Research from Microsoft and Mandiant revealed nation state groups from China, North Korea and Turkey also taking advantage of the Log4J vulnerability to deploy malware on target systems [5].  

If Log4j taught us anything, it’s that vulnerabilities in open-source technologies can be highly attractive target for nation states. When these technologies are universally adopted, geopolitical adversaries have a much wider net of opportunity to successfully weaponize them.  

It therefore comes as no surprise that nation states have ramped up their operations targeting the open-source link of the supply chain in recent years.  

Since 2020, there has been a 1300% increase in malicious threats circulating on open-source repositories. PyPI is the official open-source code repository for programming done in the Python language and used by over 800,000 developers worldwide. In the first 9 months of 2023 alone, 7,000 malicious packages were found on PyPI, some of which were linked to the North Korea state-sponsored threat group, Lazarus [6].  

Most of them were found using a technique called typosquatting, in which the malicious payloads are disguised with names that very closely resemble those of legitimate packages, ready for download by an unwitting software developer. This trickery of the eye is an example of social engineering in the supply chain.  

A hop, skip, and a jump into the most sensitive networks on earth

One of the most high-profile supply chain attacks in recent history occurred in 2023, targeting 3CX’s Desktop App – a widely used video communications by over 600,000 customers in various sectors such as aerospace, healthcare and hospitality.

The incident gained notoriety as a double supply chain attack. The initial breach originated from financial trading software called X_Trader, which had been infected with a backdoor.  A 3CX employee unknowingly downloaded the compromised X_Trader software onto a corporate device. This allowed attackers to steal the employee’s credentials and use them to gain access to 3CX’s network, spread laterally and compromising Windows and Mac systems.  

The attack moved along another link of the supply chain to several of 3CX’s customers, impacting critical national infrastructure like energy sector in US and Europe.  

For the average software provider, this attack shed more light on how a compromise of their technology could cause chaos for their customers.  

But nation states already knew this. The 3CX attack was attributed, yet again, to Lazarus, the same North Korean nation state blamed for implanting malicious packages in the Python repository.  

It’s also worth mentioning the astounding piece of evidence in a separate social engineering campaign which linked the 3CX hack to North Korea. It was an attack worthy of a Hollywood cyber block buster. The threat group, Lazarus, lured hopeful job candidates on LinkedIn into clicking on malicious ZIP file disguised as an attractive PDF offer for a position as a Developer at HSBC. The malware’s command and control infrastructure, journalide[.]org, was the same one discovered in the 3CX campaign.  

Though not strictly a supply chain attack, the LinkedIn campaign illustrates how nation states employ a diverse array of methods that span beyond the supply chain to achieve their goals. These sophisticated and well-resourced adversaries are adaptable and capable of repurposing their command-and-control infrastructure to orchestrate a range of attacks. This attack, along with the typosquatting attacks found in PyPI, serve as a critical reminder for security teams: supply chain attacks are often coupled with another powerful tactic – social engineering of human teams.

When the cure is worse than the disease

Updates to the software are a core pillar of cybersecurity, designed to patch vulnerabilities like Log4J and ensure it is safe. However, they have also proven to serve as alarmingly efficient delivery vessels for nation states to propagate their cyberattacks.  

Two of the most prolific supply chain breaches in recent history have been deployed through malicious updates, illustrating how they can be a double-edged sword when it comes to cyber defense.  

NotPetya (2017) and Solarwinds (2020)

The 2017 NotPetya ransomware attack exemplified the mass spread of ransomware via a single software update. A Russian military group injected malware on accounting software used by Ukrainian businesses for tax reporting. Via an automatic update, the ransomware was pushed out to thousands of customers within hours, crippled Ukrainian infrastructure including airports, financial institutions and government agencies.  

Some of the hardest hit victims were suppliers themselves. Maersk, the global shipping giant responsible for shipping one fifth of the world’s goods, had their entire global operations brought to a halt and their 76 ports temporarily shut down. The interruptions to global trade were then compounded when a FedEx subsidiary was hit by the same ransomware. Meanwhile, Merck, a pharmaceutical company, was unable to supply vaccines to the Center for Disease Control and Prevention due to the attack.  

In 2020, another devastating supply chain attack unfolded in a similar way. Threat actors tied to Russian intelligence embedded malicious code into Solarwinds’ Orion IT software, which was then distributed as an update to 18,000 organizations. Victims included at least eight U.S. government agencies, as well as several major tech companies.  

These two attacks highlighted two key lessons. First, in a hyperconnected digital world, nation states will exploit the trust organizations place in software updates to cause a ripple effect of devastation downstream. Secondly, the economies of scale for the threat actor themselves are staggering: a single malicious update provided the heavy lifting work of dissemination to the attacker. A colossal number of originations were infected, and they obtained the keys to the world’s most sensitive networks.

The conclusion is obvious, albeit challenging to implement; organizations must rigorously scrutinize the authenticity and security of updates to prevent far-reaching consequences.  

Some of the biggest supply chain attacks in recent history and the nation state actor they are attributed to
Figure 2: Some of the biggest supply chain attacks in recent history and the nation state actor they are attributed to

Geopolitics and nation States in 2024: Beyond the software supply chain

The threat to our increasingly complex web of global supply is real. But organizations must look beyond their software to successfully mitigate supply chain disruption. Securing hardware and logistics is crucial, as these supply chain links are also in the crosshairs of nation states.  

In July 2024, suspicious packages caused a warehouse fire at a depot belonging to courier giant DHL in Birmingham, UK. British counter-terrorism authorities investigated Russian involvement in this fire, which was linked to a very similar incident that same month at a DHL facility in Germany.  

In September 2024, camouflaged explosives were hidden in walkie talkies and pagers in Lebanon and Syria – a supply chain attack widely believed to be carried out by Israel.

While these attacks targeted hardware and logistics rather than software, the underlying rule of thumb remained the same: the compromise of a single distributor can provide the attackers with considerable economies of scale.

These attacks sparked growing concerns of coordinated efforts to sabotage the supply chain. This sentiment was reflected in a global survey carried out by HP in August 2024, in which many organisations reported “nation-state threat actors targeting physical supply chains and tampering with device hardware and firmware integrity” [7].

More recently, in November 2024, the Russian military unit 29155 vowed to “turn the lights out for millions” by threatening to launch cyberattacks on the blood supply of NATO countries, critical national infrastructure (CNI). Today, CNI encompasses more than the electric grid and water supply; it includes ICT services and IT infrastructure – the digital systems that underpin the foundations of modern society.    

This is nothing new. The supply and logistics-focused tactic has been central to warfare throughout history. What’s changed is that cyberspace has merely expanded the scale and efficiency of these tactics, turning single software compromises into attack multipliers. The supply chain threat is now more multi-faceted than ever before.  

Learnings from the supply chain threat landscape

Consider some of the most disastrous nation-state supply chain attacks in recent history – 3CX, NotPetya and Solarwinds. They share a remarkable commonality: the attackers only needed to compromise a single piece of software to cause rampant disruption. By targeting a technology provider whose products were deeply embedded across industries, threat actors leveraged the trust inherent in the supply chain to infiltrate networks at scale.

From a nation-state’s perspective, targeting a specific technology, device or service used by vast swathes of society amplifies operational efficiency. For software, hardware and critical service suppliers, these examples serve as an urgent wake-up call. Without rigorous security measures, they risk becoming conduits for global disruption. Sanity-checking code, implementing robust validation processes, and fostering a culture of security throughout the supply chain are no longer optional—they are essential.  

The stakes are clear: in the interconnected digital age, the safety of countless systems, industries and society at large depends on their vigilance.  

Screenshot of supply chain security whitepaper

Gain a deeper understanding of the evolving risks in supply chain security and explore actionable strategies to protect your organization against emerging threats. Download the white paper to empower your decision-making with expert insights tailored for CISOs

Download: Securing the Supply Chain White Paper

References

  1. https://www.gartner.com/en/documents/5524495
  1. CISA Insights “Remediate Vulnerabilities for Internet-Accessible Systems.”
  1. https://blog.checkpoint.com/security/the-numbers-behind-a-cyber-pandemic-detailed-dive/
  1. https://www.cisa.gov/news-events/cybersecurity-advisories/aa22-320a  
  1. https://www.microsoft.com/en-us/security/blog/2021/12/11/guidance-for-preventing-detecting-and-hunting-for-cve-2021-44228-log4j-2-exploitation/  
  1. https://content.reversinglabs.com/state-of-sscs-report/the-state-of-sscs-report-24  
  1. https://www.hp.com/us-en/newsroom/press-releases/2024/hp-wolf-security-study-supply-chains.html
Inside the SOC
Darktrace cyber analysts are world-class experts in threat intelligence, threat hunting and incident response, and provide 24/7 SOC support to thousands of Darktrace customers around the globe. Inside the SOC is exclusively authored by these experts, providing analysis of cyber incidents and threat trends, based on real-world experience in the field.
Written by
Benjamin Druttman
Cyber Security AI Technical Instructor

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August 21, 2025

From VPS to Phishing: How Darktrace Uncovered SaaS Hijacks through Virtual Infrastructure Abuse

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What is a VPS and how are they abused?

A Virtual Private Server (VPS) is a virtualized server that provides dedicated resources and control to users on a shared physical device.  VPS providers, long used by developers and businesses, are increasingly misused by threat actors to launch stealthy, scalable attacks. While not a novel tactic, VPS abuse is has seen an increase in Software-as-a-Service (SaaS)-targeted campaigns as it enables attackers to bypass geolocation-based defenses by mimicking local traffic, evade IP reputation checks with clean, newly provisioned infrastructure, and blend into legitimate behavior [3].

VPS providers like Hyonix and Host Universal offer rapid setup and minimal open-source intelligence (OSINT) footprint, making detection difficult [1][2]. These services are not only fast to deploy but also affordable, making them attractive to attackers seeking anonymous, low-cost infrastructure for scalable campaigns. Such attacks tend to be targeted and persistent, often timed to coincide with legitimate user activity, a tactic that renders traditional security tools largely ineffective.

Darktrace’s investigation into Hyonix VPS abuse

In May 2025, Darktrace’s Threat Research team investigated a series of incidents across its customer base involving VPS-associated infrastructure. The investigation began with a fleet-wide review of alerts linked to Hyonix (ASN AS931), revealing a noticeable spike in anomalous behavior from this ASN in March 2025. The alerts included brute-force attempts, anomalous logins, and phishing campaign-related inbox rule creation.

Darktrace identified suspicious activity across multiple customer environments around this time, but two networks stood out. In one instance, two internal devices exhibited mirrored patterns of compromise, including logins from rare endpoints, manipulation of inbox rules, and the deletion of emails likely used in phishing attacks. Darktrace traced the activity back to IP addresses associated with Hyonix, suggesting a deliberate use of VPS infrastructure to facilitate the attack.

On the second customer network, the attack was marked by coordinated logins from rare IPs linked to multiple VPS providers, including Hyonix. This was followed by the creation of inbox rules with obfuscated names and attempts to modify account recovery settings, indicating a broader campaign that leveraged shared infrastructure and techniques.

Darktrace’s Autonomous Response capability was not enabled in either customer environment during these attacks. As a result, no automated containment actions were triggered, allowing the attack to escalate without interruption. Had Autonomous Response been active, Darktrace would have automatically blocked connections from the unusual VPS endpoints upon detection, effectively halting the compromise in its early stages.

Case 1

Timeline of activity for Case 1 - Unusual VPS logins and deletion of phishing emails.
Figure 1: Timeline of activity for Case 1 - Unusual VPS logins and deletion of phishing emails.

Initial Intrusion

On May 19, 2025, Darktrace observed two internal devices on one customer environment initiating logins from rare external IPs associated with VPS providers, namely Hyonix and Host Universal (via Proton VPN). Darktrace recognized that these logins had occurred within minutes of legitimate user activity from distant geolocations, indicating improbable travel and reinforcing the likelihood of session hijacking. This triggered Darktrace / IDENTITY model “Login From Rare Endpoint While User Is Active”, which highlights potential credential misuse when simultaneous logins occur from both familiar and rare sources.  

Shortly after these logins, Darktrace observed the threat actor deleting emails referring to invoice documents from the user’s “Sent Items” folder, suggesting an attempt to hide phishing emails that had been sent from the now-compromised account. Though not directly observed, initial access in this case was likely achieved through a similar phishing or account hijacking method.

 Darktrace / IDENTITY model "Login From Rare Endpoint While User Is Active", which detects simultaneous logins from both a common and a rare source to highlight potential credential misuse.
Figure 2: Darktrace / IDENTITY model "Login From Rare Endpoint While User Is Active", which detects simultaneous logins from both a common and a rare source to highlight potential credential misuse.

Case 2

Timeline of activity for Case 2 – Coordinated inbox rule creation and outbound phishing campaign.
Figure 3: Timeline of activity for Case 2 – Coordinated inbox rule creation and outbound phishing campaign.

In the second customer environment, Darktrace observed similar login activity originating from Hyonix, as well as other VPS providers like Mevspace and Hivelocity. Multiple users logged in from rare endpoints, with Multi-Factor Authentication (MFA) satisfied via token claims, further indicating session hijacking.

Establishing control and maintaining persistence

Following the initial access, Darktrace observed a series of suspicious SaaS activities, including the creation of new email rules. These rules were given minimal or obfuscated names, a tactic often used by attackers to avoid drawing attention during casual mailbox reviews by the SaaS account owner or automated audits. By keeping rule names vague or generic, attackers reduce the likelihood of detection while quietly redirecting or deleting incoming emails to maintain access and conceal their activity.

One of the newly created inbox rules targeted emails with subject lines referencing a document shared by a VIP at the customer’s organization. These emails would be automatically deleted, suggesting an attempt to conceal malicious mailbox activity from legitimate users.

Mirrored activity across environments

While no direct lateral movement was observed, mirrored activity across multiple user devices suggested a coordinated campaign. Notably, three users had near identical similar inbox rules created, while another user had a different rule related to fake invoices, reinforcing the likelihood of a shared infrastructure and technique set.

Privilege escalation and broader impact

On one account, Darktrace observed “User registered security info” activity was shortly after anomalous logins, indicating attempts to modify account recovery settings. On another, the user reset passwords or updated security information from rare external IPs. In both cases, the attacker’s actions—including creating inbox rules, deleting emails, and maintaining login persistence—suggested an intent to remain undetected while potentially setting the stage for data exfiltration or spam distribution.

On a separate account, outbound spam was observed, featuring generic finance-related subject lines such as 'INV#. EMITTANCE-1'. At the network level, Darktrace / NETWORK detected DNS requests from a device to a suspicious domain, which began prior the observed email compromise. The domain showed signs of domain fluxing, a tactic involving frequent changes in IP resolution, commonly used by threat actors to maintain resilient infrastructure and evade static blocklists. Around the same time, Darktrace detected another device writing a file named 'SplashtopStreamer.exe', associated with the remote access tool Splashtop, to a domain controller. While typically used in IT support scenarios, its presence here may suggest that the attacker leveraged it to establish persistent remote access or facilitate lateral movement within the customer’s network.

Conclusion

This investigation highlights the growing abuse of VPS infrastructure in SaaS compromise campaigns. Threat actors are increasingly leveraging these affordable and anonymous hosting services to hijack accounts, launch phishing attacks, and manipulate mailbox configurations, often bypassing traditional security controls.

Despite the stealthy nature of this campaign, Darktrace detected the malicious activity early in the kill chain through its Self-Learning AI. By continuously learning what is normal for each user and device, Darktrace surfaced subtle anomalies, such as rare login sources, inbox rule manipulation, and concurrent session activity, that likely evade traditional static, rule-based systems.

As attackers continue to exploit trusted infrastructure and mimic legitimate user behavior, organizations should adopt behavioral-based detection and response strategies. Proactively monitoring for indicators such as improbable travel, unusual login sources, and mailbox rule changes, and responding swiftly with autonomous actions, is critical to staying ahead of evolving threats.

Credit to Rajendra Rushanth (Cyber Analyst), Jen Beckett (Cyber Analyst) and Ryan Traill (Analyst Content Lead)

References

·      1: https://cybersecuritynews.com/threat-actors-leveraging-vps-hosting-providers/

·      2: https://threatfox.abuse.ch/asn/931/

·      3: https://www.cyfirma.com/research/vps-exploitation-by-threat-actors/

Appendices

Darktrace Model Detections

•   SaaS / Compromise / Unusual Login, Sent Mail, Deleted Sent

•   SaaS / Compromise / Suspicious Login and Mass Email Deletes

•   SaaS / Resource / Mass Email Deletes from Rare Location

•   SaaS / Compromise / Unusual Login and New Email Rule

•   SaaS / Compliance / Anomalous New Email Rule

•   SaaS / Resource / Possible Email Spam Activity

•   SaaS / Unusual Activity / Multiple Unusual SaaS Activities

•   SaaS / Unusual Activity / Multiple Unusual External Sources For SaaS Credential

•   SaaS / Access / Unusual External Source for SaaS Credential Use

•   SaaS / Compromise / High Priority Login From Rare Endpoint

•   SaaS / Compromise / Login From Rare Endpoint While User Is Active

List of Indicators of Compromise (IoCs)

Format: IoC – Type – Description

•   38.240.42[.]160 – IP – Associated with Hyonix ASN (AS931)

•   103.75.11[.]134 – IP – Associated with Host Universal / Proton VPN

•   162.241.121[.]156 – IP – Rare IP associated with phishing

•   194.49.68[.]244 – IP – Associated with Hyonix ASN

•   193.32.248[.]242 – IP – Used in suspicious login activity / Mullvad VPN

•   50.229.155[.]2 – IP – Rare login IP / AS 7922 ( COMCAST-7922 )

•   104.168.194[.]248 – IP – Rare login IP / AS 54290 ( HOSTWINDS )

•   38.255.57[.]212 – IP – Hyonix IP used during MFA activity

•   103.131.131[.]44 – IP – Hyonix IP used in login and MFA activity

•   178.173.244[.]27 – IP – Hyonix IP

•   91.223.3[.]147 – IP – Mevspace Poland, used in multiple logins

•   2a02:748:4000:18:0:1:170b[:]2524 – IPv6 – Hivelocity VPS, used in multiple logins and MFA activity

•   51.36.233[.]224 – IP – Saudi ASN, used in suspicious login

•   103.211.53[.]84 – IP – Excitel Broadband India, used in security info update

MITRE ATT&CK Mapping

Tactic – Technique – Sub-Technique

•   Initial Access – T1566 – Phishing

                       T1566.001 – Spearphishing Attachment

•   Execution – T1078 – Valid Accounts

•   Persistence – T1098 – Account Manipulation

                       T1098.002 – Exchange Email Rules

•   Command and Control – T1071 – Application Layer Protocol

                       T1071.001 – Web Protocols

•   Defense Evasion – T1036 – Masquerading

•   Defense Evasion – T1562 – Impair Defenses

                       T1562.001 – Disable or Modify Tools

•   Credential Access – T1556 – Modify Authentication Process

                       T1556.004 – MFA Bypass

•   Discovery – T1087 – Account Discovery

•      Impact – T1531 – Account Access Removal

The content provided in this blog is published by Darktrace for general informational purposes only and reflects our understanding of cybersecurity topics, trends, incidents, and developments at the time of publication. While we strive to ensure accuracy and relevance, the information is provided “as is” without any representations or warranties, express or implied. Darktrace makes no guarantees regarding the completeness, accuracy, reliability, or timeliness of any information presented and expressly disclaims all warranties.

Nothing in this blog constitutes legal, technical, or professional advice, and readers should consult qualified professionals before acting on any information contained herein. Any references to third-party organizations, technologies, threat actors, or incidents are for informational purposes only and do not imply affiliation, endorsement, or recommendation.

Darktrace, its affiliates, employees, or agents shall not be held liable for any loss, damage, or harm arising from the use of or reliance on the information in this blog.

The cybersecurity landscape evolves rapidly, and blog content may become outdated or superseded. We reserve the right to update, modify, or remove any content without notice.

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Rajendra Rushanth
Cyber Analyst

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August 15, 2025

From Exploit to Escalation: Tracking and Containing a Real-World Fortinet SSL-VPN Attack

Fortinet SSL-VPN AttackDefault blog imageDefault blog image

Threat actors exploiting Fortinet CVEs

Over the years, Fortinet has issued multiple alerts about a wave of sophisticated attacks targeting vulnerabilities in its SSL-VPN infrastructure. Despite the release of patches to address these vulnerabilities, threat actors have continued to exploit a trio of Common Vulnerabilities and Exposures (CVEs) disclosed between 2022 and 2024 to gain unauthorized access to FortiGate devices.

Which vulnerabilities are exploited?

The vulnerabilities—CVE-2022-42475, CVE-2023-27997, and CVE-2024-21762—affect Fortinet’s SSL-VPN services and have been actively exploited by threat actors to establish initial access into target networks.

The vulnerabilities affect core components of FortiOS, allowing attackers to execute remote code on affected systems.

CVE-2022-42475

Type: Heap-Based Buffer Overflow in FortiOS SSL-VPN

Impact: Remote Code Execution (Actively Exploited)

This earlier vulnerability also targets the SSL-VPN interface and has been actively exploited in the wild. It allows attackers to execute arbitrary code remotely by overflowing a buffer in memory, often used to deploy malware or establish persistent backdoors [6].

CVE-2023-27997

Type: Heap-Based Buffer Overflow in FortiOS and FortiProxy

Impact: Remote Code Execution

This flaw exists in the SSL-VPN component of both FortiOS and FortiProxy. By exploiting a buffer overflow in the heap memory, attackers can execute malicious code remotely. This vulnerability is particularly dangerous because it can be triggered without authentication, making it ideal for an initial compromise [5].

CVE-2024-21762

Type: Out-of-Bounds Write in sslvpnd

Impact: Remote Code Execution

This vulnerability affects the SSL-VPN daemon (sslvpnd) in FortiOS. It allows unauthenticated remote attackers to send specially crafted HTTP requests that write data outside of allocated memory bounds. This can lead to arbitrary code execution, giving attackers full control over a device [4].

In short, these flaws enable remote attackers to execute arbitrary code without authentication by exploiting memory corruption issues such as buffer overflows and out-of-bounds writes. Once inside, threat actors use symbolic link (symlink) in order to maintain persistence on target devices across patches and firmware updates. This persistence then enables them to bypass security controls and manipulate firewall configurations, effectively turning patched systems into long-term footholds for deeper network compromise [1][2][3].

Darktrace’s Coverage

Darktrace detected a series of suspicious activities originating from a compromised Fortinet VPN device, including anomalous HTTP traffic, internal network scanning, and SMB reconnaissance, all indicative of post-exploitation behavior. Following initial detection by Darktrace’s real-time models, its Autonomous Response capability swiftly acted on the malicious activity, blocking suspicious connections and containing the threat before further compromise could occur.

Further investigation by Darktrace’s Threat Research team uncovered a stealthy and persistent attack that leveraged known Fortinet SSL-VPN vulnerabilities to facilitate lateral movement and privilege escalation within the network.

Phase 1: Initial Compromise – Fortinet VPN Exploitation

The attack on a Darktrace customer likely began on April 11 with the exploitation of a Fortinet VPN device running an outdated version of FortiOS. Darktrace observed a high volume of HTTP traffic originating from this device, specifically targeting internal systems. Notably, many of these requests were directed at the /cgi-bin/ directory,  a common target for attackers attempting to exploit web interfaces to run unauthorized scripts or commands. This pattern strongly indicated remote code execution attempts via the SSL-VPN interface [7].

Once access was gained, the threat actor likely modified existing firewall rules, a tactic often used to disable security controls or create hidden backdoors for future access. While Darktrace does not have direct visibility into firewall configuration changes, the surrounding activity and post-exploitation behavior indicated that such modifications were made to support long-term persistence within the network.

HTTP activity from the compromised Fortinet device, including repeated requests to /cgi-bin/ over port 8080.
Figure 1: HTTP activity from the compromised Fortinet device, including repeated requests to /cgi-bin/ over port 8080

Phase 2: Establishing Persistence & Lateral Movement

Shortly after the initial compromise of the Fortinet VPN device, the threat actor began to expand their foothold within the internal network. Darktrace detected initial signs of network scanning from this device, including the use of Nmap to probe the internal environment, likely in an attempt to identify accessible services and vulnerable systems.

Darktrace’s detection of unusual network scanning activities on the affected device.
Figure 2: Darktrace’s detection of unusual network scanning activities on the affected device.

Around the same time, Darktrace began detecting anomalous activity on a second device, specifically an internal firewall interface device. This suggested that the attacker had established a secondary foothold and was leveraging it to conduct deeper reconnaissance and move laterally through the network.

In an effort to maintain persistence within the network, the attackers likely deployed symbolic links in the SSL-VPN language file directory on the Fortinet device. While Darktrace did not directly observe symbolic link abuse, Fortinet has identified this as a known persistence technique in similar attacks [2][3]. Based on the observed post-exploitation behavior and likely firewall modifications, it is plausible that such methods were used here.

Phase 3: Internal Reconnaissance & Credential Abuse

With lateral movement initiated from the internal firewall interface device, the threat actor proceeded to escalate their efforts to map the internal network and identify opportunities for privilege escalation.

Darktrace observed a successful NTLM authentication from the internal firewall interface to the domain controller over the outdated protocol SMBv1, using the account ‘anonymous’. This was immediately followed by a failed NTLM session connection using the hostname ‘nmap’, further indicating the use of Nmap for enumeration and brute-force attempts. Additional credential probes were also identified around the same time, including attempts using the credential ‘guest’.

Darktrace detection of a series of login attempts using various credentials, with a mix of successful and unsuccessful attempts.
Figure 3: Darktrace detection of a series of login attempts using various credentials, with a mix of successful and unsuccessful attempts.

The attacker then initiated DCE_RPC service enumeration, with over 300 requests to the Endpoint Mapper endpoint on the domain controller. This technique is commonly used to discover available services and their bindings, often as a precursor to privilege escalation or remote service manipulation.

Over the next few minutes, Darktrace detected more than 1,700 outbound connections from the internal firewall interface device to one of the customer’s subnets. These targeted common services such as FTP (port 21), SSH (22), Telnet (23), HTTP (80), and HTTPS (443). The threat actor also probed administrative and directory services, including ports 135, 137, 389, and 445, as well as remote access via RDP on port 3389.

Further signs of privilege escalation attempts were observed with the detection of over 300 Netlogon requests to the domain controller. Just over half of these connections were successful, indicating possible brute-force authentication attempts, credential testing, or the use of default or harvested credentials.

Netlogon and DCE-RPC activity from the affected device, showing repeated service bindings to epmapper and Netlogon, followed by successful and failed NetrServerAuthenticate3 attempts.
Figure 4: Netlogon and DCE-RPC activity from the affected device, showing repeated service bindings to epmapper and Netlogon, followed by successful and failed NetrServerAuthenticate3 attempts.

Phase 4: Privilege Escalation & Remote Access

A few minutes later, the attacker initiated an RDP session from the internal firewall interface device to an internal server. The session lasted over three hours, during which more than 1.5MB of data was uploaded and over 5MB was downloaded.

Notably, no RDP cookie was observed during this session, suggesting manual access, tool-less exploitation, or a deliberate attempt to evade detection. While RDP cookie entries were present on other occasions, none were linked to this specific session—reinforcing the likelihood of stealthy remote access.

Additionally, multiple entries during and after this session show SSL certificate validation failures on port 3389, indicating that the RDP connection may have been established using self-signed or invalid certificates, a common tactic in unauthorized or suspicious remote access scenarios.

Darktrace’s detection of an RDP session from the firewall interface device to the server, lasting over 3 hours.
Figure 5: Darktrace’s detection of an RDP session from the firewall interface device to the server, lasting over 3 hours.

Darktrace Autonomous Response

Throughout the course of this attack, Darktrace’s Autonomous Response capability was active on the customer’s network. This enabled Darktrace to autonomously intervene by blocking specific connections and ports associated with the suspicious activity, while also enforcing a pre-established “pattern of life” on affected devices to ensure they were able to continue their expected business activities while preventing any deviations from it. These actions were crucial in containing the threat and prevent further lateral movement from the compromised device.

Darktrace’s Autonomous Response targeted specific connections and restricted affected devices to their expected patterns of life.
Figure 6: Darktrace’s Autonomous Response targeted specific connections and restricted affected devices to their expected patterns of life.

Conclusion

This incident highlights the importance of important staying on top of patching and closely monitoring VPN infrastructure, especially for internet-facing systems like Fortinet devices. Despite available patches, attackers were still able to exploit known vulnerabilities to gain access, move laterally and maintain persistence within the customer’s network.

Attackers here demonstrated a high level of stealth and persistence. Not only did they gain access to the network and carry out network scans and lateral movement, but they also used techniques such as symbolic link abuse, credential probing, and RDP sessions without cookies to avoid detection.  Darktrace’s detection of the post-exploitation activity, combined with the swift action of its Autonomous Response technology, successfully blocked malicious connections and contained the attack before it could escalate

Credit to Priya Thapa (Cyber Analyst), Vivek Rajan (Cyber Analyst), and Ryan Traill (Analyst Content Lead)

Appendices

Real-time Detection Model Alerts

·      Device / Suspicious SMB Scanning Activity

·      Device / Anomalous Nmap Activity

·      Device / Network Scan

·      Device / RDP Scan

·      Device / ICMP Address Scan

Autonomous Response Model Alerts:  

·      Antigena / Network / Insider Threat / Antigena Network Scan Block

·       Antigena / Network / Significant Anomaly / Antigena Significant Anomaly from Client Block

MITRE ATT&CK Mapping

Initial Access – External Remote Services – T1133

Initial Access – Valid Accounts – T1078

Execution – Exploitation for Client Execution – T1203

Persistence – Account Manipulation – T1098

Persistence – Application Layer Protocol – T1071.001

Privilege Escalation – Exploitation for Privilege Escalation – T1068

Privilege Escalation – Valid Accounts – T1078

Defense Evasion – Masquerading – T1036

Credential Access – Brute Force – T1110

Discovery – Network Service Scanning – T1046

Discovery – Remote System Discovery – T1018

Lateral Movement – Remote Services – T1021

Lateral Movement – Software Deployment Tools – T1072

Collection – Data from Local System – T1005

Collection – Data Staging – T1074

Exfiltration – Exfiltration Over Alternative Protocol – T1048

References

[1]  https://www.tenable.com/blog/cve-2024-21762-critical-fortinet-fortios-out-of-bound-write-ssl-vpn-vulnerability

[2] https://thehackernews.com/2025/04/fortinet-warns-attackers-retain.html

[3] https://www.cisa.gov/news-events/alerts/2025/04/11/fortinet-releases-advisory-new-post-exploitation-technique-known-vulnerabilities

[4] https://www.fortiguard.com/psirt/FG-IR-24-015

[5] https://www.tenable.com/blog/cve-2023-27997-heap-based-buffer-overflow-in-fortinet-fortios-and-fortiproxy-ssl-vpn-xortigate

[6]  https://www.tenable.com/blog/cve-2022-42475-fortinet-patches-zero-day-in-fortios-ssl-vpns

[7] https://www.fortiguard.com/encyclopedia/ips/12475

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About the author
Priya Thapa
Cyber Analyst
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