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November 4, 2020

Mimecast Link Rewriting: A False Sense of Security Exposed

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04
Nov 2020
Gain insight into modern email security methods to ensure you avoid pitfalls of traditional email gateways. Learn why rewriting links isn't the best approach.

Many organizations feel secure in the knowledge that their email gateway is rewriting all of the harmful links targeting their employees. Link rewriting is a common technique that involves encoding URLs sent via email into a link that redirects the user to the gateway’s own servers. These servers contain some unique codes that then track the user and perform later checks to determine whether the link is malicious.

This blog reveals why the sense of protection this gives is a fallacy, and how rewriting links does not equate to protecting the end user from actual harm. In fact, gateways’ reliance on this technique is actually an indicator of one of their fundamental flaws: their reliance on rules and signatures of previously recognized threats, and their consequent inability to stop threats on the first encounter. The reason these tools pre-emptively rewrite links is so they can make a determination later on: with the link now pointing to their own servers, they can leverage their updated assessment of that link and block a malicious site, once more information has become available (often once ‘patient zero’ has become infected; and the damage is already done).

Email security that recognizes and blocks threats on the first encounter has no need to rewrite every link.

How to measure success

If the sheer number of links rewritten is to be our measure of success, then traditional gateways win every time. For instance, Mimecast will usually rewrite 100% of the harmful links that Antigena Email locks. In fact, it rewrites nearly 100% of all links. That even includes links pointing to trusted websites like LinkedIn and Twitter, and even emails containing links to the recipient’s own website. So when tim.cook[at]apple.com receives a link to apple.com, for example, ‘mimecast.com’ will still dominate the URL.

Some organizations suffering from low first-encounter catch rates with their gateways have responded by increasing employee education: training the human to spot the giveaways of a phishing email. With email attacks getting more targeted and sophisticated, humans should never be considered the last line of defense, and rewriting links makes the situation even worse. If you’re training your users to watch which links they’re clicking, and every one of those links reads ‘mimecast.com’, how are your users supposed to learn what’s good, bad, or sketchy when every URL looks the same?

Moreover, when Mimecast’s URL gateway is down, these rewritten links don’t work (and the same applies to protected attachments). This results in business downtime which is intolerable for businesses in these critical and challenging times.

We can see the effect of blanket rewriting through Darktrace’s user interface, which shows us the frequency of rewritten links over time. Looking back over three days, this particular customer – who was trialing Antigena Email alongside Mimecast, received 155,008 emails containing rewritten links. Of those, 1,478 were anomalous, and Darktrace’s AI acted to immediately lock those links, protecting even the first recipient from harm. The remaining 153,530 links were all unnecessarily rewritten.

Figure 1: Over 155,000 inbound emails contained rewritten Mimecast links

If it comes to actually stopping the threat when a user goes to click that rewritten link, gateway tools fail. Their reliance on legacy checks like reputation, deny-lists, and rules and signatures mean that malicious content will sometimes sit for days or weeks without any meaningful action, as the technology requires at least one – and usually many – ‘patient zeros’ before determining a URL or an attachment as malicious, and updating their deny-lists.

Let’s look at the case of an attack launched from entirely new infrastructure: from a freshly purchased domain, and containing a newly created malicious payload. None of the typical metrics legacy tools search for appear as malicious, and so of course, the threat gets through, and ‘patient zero’ is infected.

Figure 2: ‘Patient Zero’ denotes the first victim of an email attack.

It inevitably takes time for the malicious link to be recognized as malicious, and for that to be reported. By this point, large swathes of the workforce have also become infected. We can call this the ‘time to detection’.

Figure 3: The time to detection

As legacy tools then update their lists in recognition of the attack, the malware continues to infect the organization, with more users engaging in the contents of the email.

Figure 4: The legacy tool reacts

Finally, the legacy tool reacts, updating its deny-list and providing substantive action to protect the end user from harm. By this point, hundreds of users across multiple organizations may have interacted with the links in some way.

Figure 5: Many ‘patient zeros’ are required before the threat is deny-listed

Email gateways’ reliance on rewriting links is directly related to their legacy approach to detection. They do it so that later down the line, when they have updated information about a potential attack, they can take action. Until then, it’s just a rewritten link, and if clicked on, it will bring the user to whatever website was hiding underneath it.

These links are also rewritten in an attempt to grasp an understanding of what user network behavior looks like. But far from giving an accurate or in-depth picture of network activity, this method barely scratches the surface of the wider behaviors of users across the organization.

Alongside Darktrace’s Enterprise Immune System, Antigena Email can pull these insights directly from a unified, central AI engine that has complete and direct visibility over an organization’s entire digital estate – not just links accessed from emails, but network activity as a whole – and not a makeshift version where it is assumed people only visit links through emails. It also pulls insights from user behavior in the cloud and across SaaS applications – from Salesforce to Microsoft Teams.

Taking real action in real time

While gateways rewrite everything in order to leave the door open to make assessments later on, Darktrace is able to take action when it needs to – before the email poses a threat in the inbox. The technology is uniquely able to do this due to its high success rates for malicious emails seen on first encounter. And it’s able to achieve such high success rates because it takes a much more sophisticated approach to detection that uses AI to catch a threat – regardless of whether or not that threat has been seen before.

Darktrace’s understanding of ‘normal’ for the human behind email communications allows it to not only detect subtle deviations that are indicative of a cyber-threat, but respond to that threat at the point of delivery. This response is targeted, proportionate and non-disruptive, and varies according to the nature of the attack. While Darktrace’s unsupervised machine learning can accurately identify deviations from ‘normal’, its supervised machine learning models are able to classify the intention behind the email; what the attacker is trying to do (extort information, solicit a payment, harvest credentials, or convince the user to download a malicious attachment).

Crucially, organizations trialing both approaches to security find that Antigena Email consistently identifies threats that Mimecast and other tools miss. With the scale and sophistication of email attacks growing, the need for a proactive and modern approach to email security is paramount. Organizations need to ensure they are measuring their sense of protection with the right yardstick, and adopt a technology that can take meaningful action before damage is done.

Trial Antigena Email today

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.
Author
Dan Fein
VP, Product

Based in New York, Dan joined Darktrace’s technical team in 2015, helping customers quickly achieve a complete and granular understanding of Darktrace’s product suite. Dan has a particular focus on Darktrace/Email, ensuring that it is effectively deployed in complex digital environments, and works closely with the development, marketing, sales, and technical teams. Dan holds a Bachelor’s degree in Computer Science from New York University.

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March 25, 2025

Survey Findings: AI Cybersecurity Priorities and Objectives in 2025

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AI is changing the cybersecurity field, both on the offensive and defensive sides. We surveyed over 1,500 cybersecurity professionals from around the world to uncover their attitudes, understanding, and priorities when it comes to AI cybersecurity in 2025. Our full report, unearthing some telling trends, is available now.  

Download the full report to explore these findings in depth

It is clear that security professionals know their field is changing fast, and that AI will continue to influence those changes. Our survey results show that they are aware that the rise of AI will require them to adopt new tools and learn to use them effectively. Still, they aren’t always certain about how to plan for the future, or what to invest in.

The top priorities of security stakeholders for improving their defenses against AI-powered threats include augmenting their existing tool stacks with AI-powered solutions and improving integration among their security tools.

Figure 1: Year-over-year changes to the priorities of securitystakeholders.

Increasing cybersecurity staff

As was also the case last year, security stakeholders are less interested in hiring additional staff than in adding new AI-powered tools onto their existing security stacks, with only with 11% (and only 8% of executives) planning to increase cybersecurity staff in 2025.

This suggests that leaders are looking for new methods to overcome talent resource shortages.

Adding AI-powered security tools to supplement existing solutions

Executives are particularly enthusiastic about adopting AI-driven tools. Within that goal, there is consensus about the qualities cyber professionals are looking for when purchasing new security capabilities or replacing existing products.

  • 87% of survey respondents prefer solutions that are part of a broader platform over individual point products

These results are similar to last year’s, where again, almost nine out of ten agreed that a platform-oriented security solution was more effective at stopping cyber threats than a collection of individual products.

  • 88% of survey respondents agree that the use of AI within the security stack is critical to freeing up time for security teams to become more proactive, compared to reactive

AI itself can contribute to this shift from reactive to proactive security, improving risk prioritization and automating preventative strategies like Attack Surface Management (ASM) and proactive exposure management.

  • 84% of survey respondents prefer defensive AI solutions that do not require the organization’s data to be shared externally

This preference may reflect increasing attention to the data privacy and security risks posed by generative AI (gen AI) adoption. It may also reflect growing awareness of data residency requirements and other restrictions that regulators are imposing.

Improving cybersecurity awareness training for end users

Based on the survey results, practitioners in SecOps are more interested in improving security awareness training.

This goal is not necessarily mutually exclusive from the addition of AI tools. For example, teams can leverage AI to build more effective security awareness training programs, and as gen AI tools are adopted, users will need to be taught about data privacy and associated security risks.

Looking towards the future

One conclusion we can draw from the attitudinal shifts from last year’s survey to this year’s: while hiring more security staff might be a nice-to-have, implementing AI-powered tools so that existing employees can work smarter is increasingly viewed as a must-have.

However, trending goals are not just about managing resources, whether headcount or AI investments, to keep up with workloads. Existing end users must also be trained to follow safe practices while using established and newly adopted tools.

Security professionals, including executives, SecOps, and every role in between, continue to shift their identified challenges and priorities as they gear up for the coming year in the Era of AI.

State of AI report

Download the full report to explore these findings in depth

The full report for Darktrace’s State of AI Cybersecurity is out now. Download the paper to dig deeper into these trends, and see how results differ by industry, region, organization size, and job title.  

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March 21, 2025

Cyberhaven Supply Chain Attack: Exploiting Browser Extensions

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The evolution of supply chain attacks

Supply chain attacks are becoming increasingly sophisticated. As network defenses improve, threat actors continuously adapt and refine their tactics, techniques, and procedures (TTPs) to achieve their goals. In recent years, this has led to a rise in the exploitation of trusted services and software, including legitimate browser extensions. Exploitation of these extensions can provide adversaries with a stealthy means to infiltrate target networks and access high-value accounts undetected.

A notable example of this trend was the compromise of the Cyberhaven Chrome extension at the end of 2024. This incident appeared to be part of a broader campaign targeting multiple Chrome browser extensions, highlighting the evolving nature of supply chain attacks [1].

What is Cyberhaven?

Cyberhaven, a US-based data security organization, experienced a security breach on December 24, 2024, when a phishing attack reportedly compromised one of their employee's credentials [2]. This allowed attackers to publish a malicious version of the Cyberhaven Chrome extension, which exfiltrated cookies and authenticated sessions from targeted websites. The malicious extension was active from December 25 to December 26 – a time when most businesses and employees were out of office and enjoying the festive period, a fact not lost on threat actors. The attackers, likely a well-organized and financially motivated group, compromised more than 30 additional Chrome extensions, affecting more than 2.6 million users [3]. They used sophisticated phishing techniques to authorize malicious OAuth applications, bypassing traditional security measures and exploiting vulnerabilities in OAuth authorizations. The primary motive appeared to be financial gain, targeting high-value platforms like social media advertising and AI services [4].

In late December 2024, multiple Darktrace customers were compromised via the Cyberhaven Chrome extension; this blog will primarily focus on Darktrace / NETWORK detections from one affected customer.

Darktrace’s coverage of Cyberhaven compromises

On December 26, 2024, Darktrace identified a series of suspicious activities across multiple customer environments, uncovering a structured attack sequence that progressed from initial intrusion to privilege escalation and data exfiltration. The attack was distributed through a malicious update to the Cyberhaven Chrome extension [2]. The malicious update established a foothold in customer environments almost immediately, leading to further anomalies.

As with other Chrome browser extensions, Cyberhaven Chrome extensions were updated automatically with no user interaction required. However, in this instance, the automatic update included a malicious version which was deployed to customer environments. This almost immediately introduced unauthorized activity, allowing attackers to establish a foothold in customer networks. The update allowed attackers to execute their objectives in the background, undetected by traditional security tools that rely on known indicators of compromise (IoCS) rather than identifying anomalies.

While multiple customer devices were seen connecting to cyberhaven[.]io, a legitimate Cyberhaven domain, Darktrace detected persistent beaconing behavior to cyberhavenext[.]pro, which appeared to be attempting to masquerade as another legitimate Cyberhaven domain. Darktrace recognized this activity as unusual, triggering several model alerts in Darktrace / NETWORK to highlight the persistent outbound connections to the suspicious domain.

Further analysis of external connectivity patterns indicated  an increase in anomalous HTTP requests alongside this beaconing activity. Multiple open-source intelligence (OSINT) sources also suggest that the cyberhavenext[.]pro endpoint is associated with malicious activities [5].

Darktrace / NETWORK’s detection of beaconing activity to cyberhavenext[.]pro
Figure 1: Darktrace / NETWORK’s detection of beaconing activity to cyberhavenext[.]pro

Analysis using Darktrace’s Advanced Search revealed that some of these connections were directed to the suspicious external IP address 149.28.124[.]84. Further investigation confirmed that the IP correlated with two SSL hostnames, including the malicious cyberhavenext[.]pro, further reinforcing its connection to the attack infrastructure.

Darktrace Advanced Search analysis showing the IP address 149.28.124[.]84 correlating to two SSL hostnames, one of which is cyberhavenext[.]pro.
Figure 2: Darktrace Advanced Search analysis showing the IP address 149.28.124[.]84 correlating to two SSL hostnames, one of which is cyberhavenext[.]pro.

Between December 23 and December 27, Darktrace observed sustained beaconing-like activity from affected devices on the customer’s network.

Darktrace’s detection of beaconing activities from a customer device to the endpoint 149.28.124[.]84 between December 23 and December 27.
Figure 3: Darktrace’s detection of beaconing activities from a customer device to the endpoint 149.28.124[.]84 between December 23 and December 27.

Darktrace observed 27 unique devices connecting to the malicious command-and-control (C2) infrastructure as far back as December 3. While most connections were brief, they represented an entry point for malicious activity. Over a two-day period, two devices transmitted 5.57 GiB of incoming data and 859.37 MiB of outgoing data, generating over 3 million log events across SSL, HTTP, and connection data.

Subsequent analysis identified a significant increase in unauthorized data transfers to the aforementioned 149.28.124[.]84 IP on another customer network, highlighting the potential broader impact of this compromise. The volume and frequency of these transfers suggested that attackers were leveraging automated data collection techniques, further underscoring the sophistication of the attack.

Darktrace’s detection of the likely exfiltration of 859.37 MiB to the endpoint 149.28.124[.]84.
Figure 4: Darktrace’s detection of the likely exfiltration of 859.37 MiB to the endpoint 149.28.124[.]84.

External research suggested that once active, the Cyberhaven extension would begin silently collecting session cookies and authentication tokens, specifically targeting high-value accounts such as Facebook Ads accounts [4]. Darktrace’s analysis of another affected customer noted many HTTP POST connections directed to a specific URI ("ai-cyberhaven"), while GET requests contained varying URIs prefixed with "/php/urlblock?args=AAAh....--redirect." This activity indicated an exfiltration mechanism, consistent with techniques observed in other compromised Chrome extensions. By compromising session cookies, attackers could potentially gain administrative access to connected accounts, further escalating their privileges [4].

Conclusion

This incident highlights the importance of monitoring not just endpoint security, but also cloud and browser-based security solutions, as attackers increasingly target these trusted and oft overlooked vectors.

Ultimately, by focusing on anomaly detection and behavioral analysis rather than static signatures and lists of ‘known bads’, Darktrace was able to successfully detect devices affected by the Cyberhaven Chrome browser extension compromise, by identifying activity that would likely have been considered legitimate and benign by traditional security solutions.

This compromise also serves as a reminder that supply chain attacks are not limited to traditional software vendors. Browser extensions, cloud-based applications, and SaaS services are equally vulnerable, as evidenced by Darktrace's detection of Balada Injector malware exploiting WordPress vulnerabilities to gain unauthorized network access [6]. Therefore, increased targeting of browser-based security tools, and a greater exploitation of OAuth and session hijacking techniques are to be expected. Attackers will undoubtedly refine their methods to infiltrate legitimate vendors and distribute malicious updates through trusted channels. By staying informed, vigilant, and proactive, organizations can mitigate exposure to evolving supply chain threats and safeguard their critical assets from emerging browser-based attack techniques.

Credit to Rajendra Rushanth (Cyber Analyst) Justin Torres (Senior Cyber Analyst) and Ryan Traill (Analyst Content Lead)

Appendices

Darktrace Model Detections

·       Compromise / Beaconing Activity To External Rare (AP: C2 Comms)

·       Compromise / Beacon for 4 Days (AP: C2 Comms)

·       Compromise / HTTP Beaconing to Rare Destination (AP: C2 Comms)

·       Device / Suspicious Domain (AP: C2 Comms, AP: Tooling)

·       Compromise / Sustained TCP Beaconing Activity To Rare Endpoint (AP: C2 Comms)

·       Anomalous Server Activity / Rare External from Server (AP: C2 Comms)

·       Anomalous Connection / Multiple Failed Connections to Rare Endpoint (AP: C2 Comms)

·       Anomalous Server Activity / Anomalous External Activity from Critical Network Device (AP: C2 Comms)

·       Compromise / Slow Beaconing Activity To External Rare (AP: C2 Comms)

·       Compromise / Repeating Connections Over 4 Days (AP: C2 Comms)

·       Anomalous Connection / Multiple HTTP POSTs to Rare Hostname (AP: C2 Comms)

·       Anomalous Server Activity / Outgoing from Server (AP: C2 Comms)

·       Compromise / High Volume of Connections with Beacon Score (AP: C2 Comms)

·       Compromise / Large Number of Suspicious Failed Connections (AP: C2 Comms)

·       Email Nexus / Connection to Hijacked Correspondent Link

·       Compromise / Suspicious TLS Beaconing To Rare External (AP: C2 Comms)

·       Compromise / Quick and Regular Windows HTTP Beaconing (AP: C2 Comms)

List of IoCs

IoC - Type - Description + Confidence

cyberhavenext[.]pro - Hostname - Used for C2 communications and data exfiltration (cookies and session tokens)

149.28.124[.]84 - IP - Associated with malicious infrastructure

45.76.225[.]148 - IP - Associated with malicious infrastructure

136.244.115[.]219 - IP - Associated with malicious infrastructure

MITRE ATT&CK Mapping

Tactic – Technique – Sub-Technique

INITIAL ACCESS - T1176 - Browser Extensions

EXECUTION - T1204.002 - Malicious Browser Extensions

PERSISTENCE - T1176 - Browser Extensions

COMMAND AND CONTROL - T1071.001 - Web Protocols

COMMAND AND CONTROL - T1001 - Data Obfuscation

CREDENTIAL ACCESS - T1539 - Steal Web Session Cookie

DISCOVERY - T1518.001 - Security Software Discovery

LATERAL MOVEMENT - T1557.003 - Man-in-the-Browser

EXFILTRATION - T1041 - Exfiltration Over C2 Channel

EXFILTRATION - T1567.002 - Exfiltration to Cloud Storage

IMPACT - T1583.006 - Session Hijacking

References

[1] https://thehackernews.com/2024/12/16-chrome-extensions-hacked-exposing.html

[2] https://www.cyberhaven.com/blog/cyberhavens-chrome-extension-security-incident-and-what-were-doing-about-it

[3] https://www.infosecurity-magazine.com/news/chrome-browser-extensions-hijacked/

[4] https://www.theverge.com/2024/12/28/24330758/chrome-extension-cyberhaven-hijack-phishing-cyberattack-facebook-ads-authentication-theft

[5] https://www.virustotal.com/gui/domain/cyberhavenext.pro

[6] https://darktrace.com/blog/balada-injector-darktraces-investigation-into-the-malware-exploiting-wordpress-vulnerabilities

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About the author
Rajendra Rushanth
Cyber Analyst
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