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August 2, 2024

Safelink Smuggling: Enhancing Resilience Against Malicious Links

Gain insights into safelink smuggling tactics and learn strategies to protect your organization from the dangers posed by malicious links.
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
Carlos Gray
Senior Product Marketing Manager, Email
Written by
Stephen Pickman
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02
Aug 2024

Darktrace security members and researchers have recently seen a rise in what we are calling Safelink Smuggling. Safelinks are URLs rewritten by security solutions to enable additional analysis when the URL is clicked. Once analyzed, they may prompt a user, redirect the browser back to the original URL, or block further access if deemed necessary.

What is Safelink Smuggling?

Safelink Smuggling is a technique that involves an attacker purposely getting their malicious payload rewritten by a security solution’s Safelink capability to then propagate the rewritten URL to others. This technique is a way for attackers to not only avoid detection by traditional email security and other solutions, but also to instill mistrust in all email security solutions. As a result, Safelinks from a range of popular email security providers are often seen in phishing or supply chain attacks. In fact, Darktrace has observed over 300,000 cases of Safelinks being included in unexpected and suspicious contexts over the last 3 months.

How does Safelink Smuggling work?

Safelink Smuggling has two key stages: Getting a malicious link rewritten by an email security solution, then propagating that rewritten link to other victims.

Step one:

Obfuscated a malicious payload through a Safelink capability rewriting the link; Darktrace has seen this attempted through two methods – Compromised Account or Reply-Chain.

  • Method 1: Compromised Account

If an attacker can gain access to a compromised account – whether that’s through brute force, malware or credential theft – they can infiltrate it with malicious links, and then exfiltrate the Safelinks created as the email passes through security filtering. In other words, attackers will send a malicious payload to the compromised inbox, with the intent that the malicious URL gets rewritten. Unlike a normal phishing email where the threat actor wants to avoid having their email blocked, in this case the objective is for the email to get through to the inbox with the link rewritten. As observed by Darktrace, attackers often send the link in isolation as any additional components (i.e., body text or other content in the email) could cause a more severe action such as the email security solution holding the message.

  • Method 2: Reply-Chain

With this method, the attacker sends a malicious link to an email security vendor’s customer in an attempt to solicit a reply from an internal user. This allows them to grab the re-written URL within the reply chain. However, this is a risky tactic which can fail at several points. The attacker has to be confident the initial email won't be blocked outright; they also risk alerting security vendors to the address and the URL intended to be used for the main campaign. They also must be confident that the checks made when the re-written URL is clicked will not lead to a block at the final destination.
Regardless of the method used, the end result will appear as follows:

For example, the original malicious URL may look like this,

faceldu[.]org/Invoice112.zip

(negative surface indicators: recently registered domain, file extension)

And after being rewritten,

securityvevndor[.]com/safe?q=aNDF80dfaAkAH930adbd

(positive surface indicators: established domain, positive reputation, associated with safe content)

Step Two:

Now that the attacker has access to a malicious URL that has been obfuscated by a safe rewrite, attackers can forward or craft an email leveraging that same link. In fact, we have even seen multiple layers of Safelink Smuggling being used to mask a payload further.

The Challenge of Link Rewriting

Traditional email security solutions rewrite all links sent to an organization, but there is an inherent risk to this methodology. Rewriting every link, whether harmless or harmful, leads employees to lose context and creates a false sense of security when interacting with rewritten links in emails. Furthermore, it provides attackers with many opportunities to exploit Safelinks. As demonstrated in Method 2 above, if an email security solution does not rewrite every link, executing such attacks would be significantly more challenging.

Traditionally, rewriting every link made sense from a security perspective, as it allowed servers to thoroughly analyze links for known attack patterns and signatures. However, this approach relies on identifying previously recognized threats. Conversely, Darktrace / EMAIL gathers sufficient information about a link without needing to rewrite it, by analyzing the context and content of the email and the link itself.

In fact, Darktrace is the pioneer in applying selective rewriting to URLs based on suspicious properties or context, a method that other solutions have since adopted. While traditional solutions rewrite links to assess them only after they are clicked, Darktrace / EMAIL takes immediate action to neutralize threats before they reach the inbox.

Darktrace achieves high success rates in detecting malicious links and emails on the first encounter using Self-Learning AI. By understanding 'normal' behavior in email communications, Darktrace identifies subtle deviations indicative of cyber threats and selectively rewrites only those links deemed suspicious, ensuring a targeted, proportionate, and non-disruptive response.

Why do traditional email security solutions miss Safelink attacks?

Traditional security solutions that focus on learning attack patterns will miss Safelink threats as they are often utilized in attacks that have a variety of layers which help the email seem legitimate. Leveraging all the classic techniques seen in a supply chain attack to disguise the sender's intent, taking advantage of the users' inherent trust in familiar sources, the user is more likely to lower their defenses.

For more information: https://darktrace.com/products/email/use-cases/supply-chain-attack

In terms of the URL, if the payload is malicious, why is it difficult for email security solutions to catch it? Primarily, other security vendors will focus on the payload in isolation, attempting to find known attack patterns or signatures such as a domain name or IP with a bad reputation. Unfortunately, with this technique, if the URL has a legitimate domain, it will return a clean track record. Common obfuscation techniques such as captchas, short-links, and click throughs can all be deployed to add layers of complexity to the analysis.

Safelink Smuggling relies heavily on link redirects, which means that web analysis tools will falter as they will only analyze the first redirect. Consequently, when more in-depth analysis on the link itself is performed, the first place the URL takes the user is not the malicious site but rather the default on-click analysis of the vendor in question. Therefore, any traditional browser or link analysis will also return a negative result.

Finally, the context itself is important. In contrast to traditional email security solutions, Darktrace / EMAIL asks who, what, when, where, and why for every single email, and compares it to the pattern of life of both the internal recipient and the external sender, rather than attempting to match patterns with historical threat data. When analyzing an email from an inbound perspective, Darktrace reveals potential deviations from normal, that, when considered sufficiently anomalous, will result in taking a proportional action to the threat assessed.

To illustrate the above, let’s take a look at an example email that Darktrace recently caught.

The following is an email a Darktrace customer received, which Darktrace / EMAIL held before it reached the inbox. In this case, the smuggled Safelink was further obfuscated behind a QR Code. The accompanying document also presented some anomalies in terms of its intent, perceived as a potential social engineering attempt. Finally, the lack of association and low mailing history meant there was no prior context for this email.  

Example of a Safelink Smuggling attack using a popular email security solution’s safelink.
Fig 1: Example of a Safelink Smuggling attack using a popular email security solution’s safelink.

How to mitigate against Safelink Smuggling?

It's difficult for email security vendors to do anything about their links being reused, and reuse should almost be expected by popular operators in the email security space. Therefore, the presence of links from a vendor’s domain in a suspicious email communication rarely indicates a compromise of the link rewrite infrastructure or a compromise of the third-party vendor.

Email security vendors can improve their defense-in-depth, especially around their email provider accounts to avoid Method 1 (Compromised Account attacks) and become more selective with their rewrites to curtail Method 2 (Reply Chain attacks).

Primary protection against Safelink Smuggling should be offered by the email security vendor responsible for inbound email analysis. They need to ensure that techniques such as Safelink Smuggling are not evaded by their detection mechanisms.

Darktrace has long been working on the betterment of security within the email community and innovating our link analysis infrastructure to mitigate against this attack methodology (read more about our major update in 6.2 here), regardless of whether the receiving organization are Darktrace customers.

How does Darktrace deal with Safelink Smuggling today?

Darktrace has been dealing with Safelink Smuggling since launch and has a standardized recommendation for customers who are looking to defend against this threat.

Customers want to avoid being 1) the propagators of this threat and potentially damaging their brand reputation, and 2) being victims of the supply chain attack thereafter.

The principal recommendation to protect customer accounts and consequently their brands is to ensure defense-in-depth. As accounts establish themselves as the crown jewels of any modern enterprise, organizations should vigilantly monitor their account activity with the same rigor they would analyze their network activity. Whether that is through the base account takeover protection offered by Darktrace / EMAIL, or the expanded defense offered by Darktrace / IDENTITY, it is crucial that the accounts themselves have a robust security solution in place.

Secondly, to avoid falling victim to the supply chain attack that leverages a third-party vendor’s link rewrite, it is imperative to use a solution that does not rely on static threat intelligence and link reputation analysis. Rather than chasing attackers by updating rules and signatures, Darktrace leverages Self-Learning AI to learn the communication patterns of both internal and external messages to reveal deviations in both content and context.

Finally, for those customers that already leverage Darktrace / EMAIL we recommend ensuring that lock links are enabled, and that the default warning page is displayed every time a link is rewritten, no matter the perceived severity of the link. This will allow any potential user that clicks on a rewritten Darktrace / EMAIL link to be alerted to the potential nature of the site they are trying to access.

Safelink smuggling example caught by Darktrace

While most cases involve other vendors, analysts recently saw a case where Darktrace's own links were used in this type of attack. A small number of links were leveraged in a campaign targeting both Darktrace and non-Darktrace customers alike. Thankfully, these attempts were all appropriately actioned by those customers that had Darktrace / EMAIL deployed.

In the example below, you will see how Darktrace Cyber AI Analyst describes the example at hand under the Anomaly Indicators section.

Example of Safelink Smuggling attack on Darktrace using the Darktrace Safelink Infrastructure.
Fig 2: Example of Safelink Smuggling attack on Darktrace using the Darktrace Safelink Infrastructure.

First, the display name mismatch can be interpreted as an indicator of social engineering, attempting to deceive the recipient with an IT policy change.

Second, the link itself, which in this case is a hidden redirect to an unusual host for this environment.

Finally, there is a suspected account takeover due to the origin of the email being a long-standing, validated domain that contains a wide variety of suspicious elements.

Darktrace / EMAIL would have held this email from being delivered.

Conclusion

By investigating Safelink Smuggling, Darktrace wants to shine a light on the technique for security teams and help raise awareness of how it can be used to dupe users into lowering their defenses. Challenge your email security vendor on how it deals with link analysis, particularly from trusted senders and applications.

Interested in Darktrace’s approach to defense-in-depth? Check out Darktrace / EMAIL

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
Carlos Gray
Senior Product Marketing Manager, Email
Written by
Stephen Pickman

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September 9, 2025

The benefits of bringing together network and email security

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In many organizations, network and email security operate in isolation. Each solution is tasked with defending its respective environment, even though both are facing the same advanced, multi-domain threats.  

This siloed approach overlooks a critical reality: email remains the most common vector for initiating cyber-attacks, while the network is the primary stage on which those attacks progress. Without direct integration between these two domains, organizations risk leaving blind spots that adversaries can exploit.  

A modern security strategy needs to unify email and network defenses, not just in name, but in how they share intelligence, conduct investigations, and coordinate response actions. Let’s take a look at how this joined-up approach delivers measurable technical, operational, and commercial benefits.

Technical advantages

Pre-alert intelligence: Gathering data before the threat strikes

Most security tools start working when something goes wrong – an unusual login, a flagged attachment, a confirmed compromise. But by then, attackers may already be a step ahead.

By unifying network and email security under a single AI platform (like the Darktrace Active AI Security Platform), you can analyze patterns across both environments in real time, even when there are no alerts. This ongoing monitoring builds a behavioral understanding of every user, device, and domain in your ecosystem.

That means when an email arrives from a suspicious domain, the system already knows whether that domain has appeared on your network before – and whether its behavior has been unusual. Likewise, when new network activity involves a domain first spotted in an email, it’s instantly placed in the right context.

This intelligence isn’t built on signatures or after-the-fact compromise indicators – it’s built on live behavioral baselines, giving your defenses the ability to flag threats before damage is done.

Alert-related intelligence: Connecting the dots in real time

Once an alert does fire, speed and context matter. The Darktrace Cyber AI Analyst can automatically investigate across both environments, piecing together network and email evidence into a single, cohesive incident.

Instead of leaving analysts to sift through fragmented logs, the AI links events like a phishing email to suspicious lateral movement on the recipient’s device, keeping the full attack chain intact. Investigations that might take hours – or even days – can be completed in minutes, with far fewer false positives to wade through.

This is more than a time-saver. It ensures defenders maintain visibility after the first sign of compromise, following the attacker as they pivot into network infrastructure, cloud services, or other targets. That cross-environment continuity is impossible to achieve with disconnected point solutions or siloed workflows.

Operational advantages

Streamlining SecOps across teams

In many organizations, email security is managed by IT, while network defense belongs to the SOC. The result? Critical information is scattered between tools and teams, creating blind spots just when you need clarity.

When email and network data flow into a single platform, everyone is working from the same source of truth. SOC analysts gain immediate visibility into email threats without opening another console or sending a request to another department. The IT team benefits from the SOC’s deeper investigative context.

The outcome is more than convenience: it’s faster, more informed decision-making across the board.

Reducing time-to-meaning and enabling faster response

A unified platform removes the need to manually correlate alerts between tools, reducing time-to-meaning for every incident. Built-in AI correlation instantly ties together related events, guiding analysts toward coordinated responses with higher confidence.

Instead of relying on manual SIEM rules or pre-built SOAR playbooks, the platform connects the dots in real time, and can even trigger autonomous response actions across both environments simultaneously. This ensures attacks are stopped before they can escalate, regardless of where they begin.

Commercial advantages

While purchasing “best-of-breed" for all your different tools might sound appealing, it often leads to a patchwork of solutions with overlapping costs and gaps in coverage. However good a “best-in-breed" email security solution might be in the email realm, it won't be truly effective without visibility across domains and an AI analyst piecing intelligence together. That’s why we think “best-in-suite" is the only “best-in-breed" approach that works – choosing a high-quality platform ensures that every new capability strengthens the whole system.  

On top of that, security budgets are under constant pressure. Managing separate vendors for email and network defense means juggling multiple contracts, negotiating different SLAs, and stitching together different support models.

With a single provider for both, procurement and vendor management become far simpler. You deal with one account team, one support channel, and one unified strategy for both environments. If you choose to layer on managed services, you get consistent expertise across your whole security footprint.

Even more importantly, an integrated AI platform sets the stage for growth. Once email and network are under the same roof, adding coverage for other attack surfaces – like cloud or identity – is straightforward. You’re building on the same architecture, not bolting on new point solutions that create more complexity.

Check out the white paper, The Modern Security Stack: Why Your NDR and Email Security Solutions Need to Work Together, to explore these benefits in more depth, with real-world examples and practical steps for unifying your defenses.

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Mikey Anderson
Product Marketing Manager, Network Detection & Response

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September 9, 2025

Unpacking the Salesloft Incident: Insights from Darktrace Observations

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Introduction

On August 26, 2025, Google Threat intelligence Group released a report detailing a widespread data theft campaign targeting the sales automation platform Salesloft, via compromised OAuth tokens used by the third-party Drift AI chat agent [1][2].  The attack has been attributed to the threat actor UNC6395 by Google Threat Intelligence and Mandiant [1].

The attack is believed to have begun in early August 2025 and continued through until mid-August 2025 [1], with the threat actor exporting significant volumes of data from multiple Salesforce instances [1]. Then sifting through this data for anything that could be used to compromise the victim’s environments such as access keys, tokens or passwords. This had led to Google Threat Intelligence Group assessing that the primary intent of the threat actor is credential harvesting, and later reporting that it was aware of in excess of 700 potentially impacted organizations [3].

Salesloft previously stated that, based on currently available data, customers that do not integrate with Salesforce are unaffected by this campaign [2]. However, on August 28, Google Threat Intelligence Group announced that “Based on new information identified by GTIG, the scope of this compromise is not exclusive to the Salesforce integration with Salesloft Drift and impacts other integrations” [2]. Google Threat Intelligence has since advised that any and all authentication tokens stored in or connected to the Drift platform be treated as potentially compromised [1].

This campaign demonstrates how attackers are increasingly exploiting trusted Software-as-a-Service (SaaS) integrations as a pathway into enterprise environment.

By abusing these integrations, threat actors were able to exfiltrate sensitive business data at scale, bypassing traditional security controls. Rather than relying on malware or obvious intrusion techniques, the adversaries leveraged legitimate credentials and API traffic that resembled legitimate Salesforce activity to achieve their goals. This type of activity is far harder to detect with conventional security tools, since it blends in with the daily noise of business operations.

The incident underscores the escalating significance of autonomous coverage within SaaS and third-party ecosystems. As businesses increasingly depend on interconnected platforms, visibility gaps become evident that cannot be managed by conventional perimeter and endpoint defenses.

By developing a behavioral comprehension of each organization's distinct use of cloud services, anomalies can be detected, such as logins from unexpected locations, unusually high volumes of API requests, or unusual document activity. These indications serve as an early alert system, even when intruders use legitimate tokens or accounts, enabling security teams to step in before extensive data exfiltration takes place

What happened?

The campaign is believed to have started on August 8, 2025, with malicious activity continuing until at least August 18. The threat actor, tracked as UNC6395, gained access via compromised OAuth tokens associated with Salesloft Drift integrations into Salesforce [1]. Once tokens were obtained, the attackers were able to issue large volumes of Salesforce API requests, exfiltrating sensitive customer and business data.

Initial Intrusion

The attackers first established access by abusing OAuth and refresh tokens from the Drift integration. These tokens gave them persistent access into Salesforce environments without requiring further authentication [1]. To expand their foothold, the threat actor also made use of TruffleHog [4], an open-source secrets scanner, to hunt for additional exposed credentials. Logs later revealed anomalous IAM updates, including unusual UpdateAccessKey activity, which suggested attempts to ensure long-term persistence and control within compromised accounts.

Internal Reconnaissance & Data Exfiltration

Once inside, the adversaries began exploring the Salesforce environments. They ran queries designed to pull sensitive data fields, focusing on objects such as Cases, Accounts, Users, and Opportunities [1]. At the same time, the attackers sifted through this information to identify secrets that could enable access to other systems, including AWS keys and Snowflake credentials [4]. This phase demonstrated the opportunistic nature of the campaign, with the actors looking for any data that could be repurposed for further compromise.

Lateral Movement

Salesloft and Mandiant investigations revealed that the threat actor also created at least one new user account in early September. Although follow-up activity linked to this account was limited, the creation itself suggested a persistence mechanism designed to survive remediation efforts. By maintaining a separate identity, the attackers ensured they could regain access even if their stolen OAuth tokens were revoked.

Accomplishing the mission

The data taken from Salesforce environments included valuable business records, which attackers used to harvest credentials and identify high-value targets. According to Mandiant, once the data was exfiltrated, the actors actively sifted through it to locate sensitive information that could be leveraged in future intrusions [1]. In response, Salesforce and Salesloft revoked OAuth tokens associated with Drift integrations on August 20 [1], a containment measure aimed at cutting off the attackers’ primary access channel and preventing further abuse.

How did the attack bypass the rest of the security stack?

The campaign effectively bypassed security measures by using legitimate credentials and OAuth tokens through the Salesloft Drift integration. This rendered traditional security defenses like endpoint protection and firewalls ineffective, as the activity appeared non-malicious [1]. The attackers blended into normal operations by using common user agents and making queries through the Salesforce API, which made their activity resemble legitimate integrations and scripts. This allowed them to operate undetected in the SaaS environment, exploiting the trust in third-party connections and highlighting the limitations of traditional detection controls.

Darktrace Coverage

Anomalous activities have been identified across multiple Darktrace deployments that appear associated with this campaign. This included two cases on customers based within the United States who had a Salesforce integration, where the pattern of activities was notably similar.

On August 17, Darktrace observed an account belonging to one of these customers logging in from the rare endpoint 208.68.36[.]90, while the user was seen active from another location. This IP is a known indicator of compromise (IoC) reported by open-source intelligence (OSINT) for the campaign [2].

Cyber AI Analyst Incident summarizing the suspicious login seen for the account.
Figure 1: Cyber AI Analyst Incident summarizing the suspicious login seen for the account.

The login event was associated with the application Drift, further connecting the events to this campaign.

Advanced Search logs showing the Application used to login.
Figure 2: Advanced Search logs showing the Application used to login.

Following the login, the actor initiated a high volume of Salesforce API requests using methods such as GET, POST, and DELETE. The GET requests targeted endpoints like /services/data/v57.0/query and /services/data/v57.0/sobjects/Case/describe, where the former is used to retrieve records based on a specific criterion, while the latter provides metadata for the Case object, including field names and data types [5,6].

Subsequently, a POST request to /services/data/v57.0/jobs/query was observed, likely to initiate a Bulk API query job for extracting large volumes of data from the Ingest Job endpoint [7,8].

Finally, a DELETE request to remove an ingestion job batch, possibly an attempt to obscure traces of prior data access or manipulation.

A case on another US-based customer took place a day later, on August 18. This again began with an account logging in from the rare IP 208.68.36[.]90 involving the application Drift. This was followed by Salesforce GET requests targeting the same endpoints as seen in the previous case, and then a POST to the Ingest Job endpoint and finally a DELETE request, all occurring within one minute of the initial suspicious login.

The chain of anomalous behaviors, including a suspicious login and delete request, resulted in Darktrace’s Autonomous Response capability suggesting a ‘Disable user’ action. However, the customer’s deployment configuration required manual confirmation for the action to take effect.

An example model alert for the user, triggered due to an anomalous API DELETE request.
Figure 3: An example model alert for the user, triggered due to an anomalous API DELETE request.
Figure 4: Model Alert Event Log showing various model alerts for the account that ultimately led to an Autonomous Response model being triggered.

Conclusion

In conclusion, this incident underscores the escalating risks of SaaS supply chain attacks, where third-party integrations can become avenues for attacks. It demonstrates how adversaries can exploit legitimate OAuth tokens and API traffic to circumvent traditional defenses. This emphasizes the necessity for constant monitoring of SaaS and cloud activity, beyond just endpoints and networks, while also reinforcing the significance of applying least privilege access and routinely reviewing OAuth permissions in cloud environments. Furthermore, it provides a wider perspective into the evolution of the threat landscape, shifting towards credential and token abuse as opposed to malware-driven compromise.

Credit to Emma Foulger (Global Threat Research Operations Lead), Calum Hall (Technical Content Researcher), Signe Zaharka (Principal Cyber Analyst), Min Kim (Senior Cyber Analyst), Nahisha Nobregas (Senior Cyber Analyst), Priya Thapa (Cyber Analyst)

Appendices

Darktrace Model Detections

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

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

·      SaaS / Compliance / Anomalous Salesforce API Event

·      SaaS / Unusual Activity / Multiple Unusual SaaS Activities

·      Antigena / SaaS / Antigena Unusual Activity Block

·      Antigena / SaaS / Antigena Suspicious Source Activity Block

Customers should consider integrating Salesforce with Darktrace where possible. These integrations allow better visibility and correlation to spot unusual behavior and possible threats.

IoC List

(IoC – Type)

·      208.68.36[.]90 – IP Address

References

1.     https://cloud.google.com/blog/topics/threat-intelligence/data-theft-salesforce-instances-via-salesloft-drift

2.     https://trust.salesloft.com/?uid=Drift+Security+Update%3ASalesforce+Integrations+%283%3A30PM+ET%29

3.     https://thehackernews.com/2025/08/salesloft-oauth-breach-via-drift-ai.html

4.     https://unit42.paloaltonetworks.com/threat-brief-compromised-salesforce-instances/

5.     https://developer.salesforce.com/docs/atlas.en-us.api_rest.meta/api_rest/resources_query.htm

6.     https://developer.salesforce.com/docs/atlas.en-us.api_rest.meta/api_rest/resources_sobject_describe.htm

7.     https://developer.salesforce.com/docs/atlas.en-us.api_asynch.meta/api_asynch/get_job_info.htm

8.     https://developer.salesforce.com/docs/atlas.en-us.api_asynch.meta/api_asynch/query_create_job.htm

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About the author
Emma Foulger
Global Threat Research Operations Lead
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