Over 300GB of data was exfiltrated from a customer network before Darktrace services intervened. Learn the power of Darktrace in autonomous mode.
Side-by-side, data loss and cyber-attacks are two of the most common concerns expressed by IT directors. Whilst ransom has traditionally been seen as a big cause of this, ransom (and subsequently) data loss appears to be changing. This blog explores an incident seen within a middle eastern financial customer from May-June 2022. This customer suffered large data loss and a high volume of files with a ransom note were written on its network, but the institution’s data was not encrypted. This is an example of a growing trend in ransomware attacks, which involves exfiltration of the victim’s data and the write of a ransom note but no encryption of files. Instead of being extorted for the decryption of their files, companies are being extorted for the return of their stolen data.
Attack Summary
A threat actor spread laterally through a customer network by writing suspicious ‘.dat’ and ‘.exe’ files, exfiltrated more than 300GB of data over a two-month period and made beaconing connections to endpoints identified by OSINT as probable Cobalt Strike C2 servers.
Attack Details
In May an internal desktop was observed connecting to a rare external endpoint over the SSL protocol using a highly unusual port and the RClone client. These connections continued for several weeks and spiked at the same time as the device’s other malicious activity. It is likely that these connections reflected a potential point of infection.
The attacker then used the desktop and two other internal devices to perform network scanning and enumeration activity in order to discover other devices on the network it could infect. In total 856 unique IPs were scanned- largely over TCP, UDP and ICMP. Further directory replication service requests were also seen over DCE-RPC, suggesting an attempt to extract user credentials. One device was later seen accessing an unencrypted password file showing successful recon. The attacker then used the already compromised devices to infect other devices on the network by writing suspicious ‘.exe’ and ‘.dat’ files including ‘Bun.dat' and ‘Agent.exe’.
The compromised devices were then used by the attacker to download nearly 4GB of data from an internal server and to upload a similar amount to a suspicious IP address associated with a young domain. Over the following two months, the compromised devices went on to upload roughly 100GB of data to the same destination each week.
The attacker also used these devices to make beaconing connections to several rare and external endpoints. Some of these endpoints were created just before the beginning of the compromise and have all been identified by OSINT as probable Cobalt Strike command and control servers. During this beaconing an internal device was also observed making an extremely large number of writes of files that appeared to be ransom notes, these were appropriately named ‘YOURNETWORKDATAHASBEENCOMPROMISED.txt’.
Darktrace Coverage
How did this attack remain hidden from the company’s other tools? Neither the initial C2 IP Address, the follow-on Cobalt Strike C2 servers or the exfiltration server were associated with malicious activity in open-source reporting prior to this compromise. This meant they were likely omitted from expected blacklists and standard signature-based security. Furthermore, executable files written by the compromised devices included ‘anydesk.exe’ and ‘procdump64.exe’, both of which are legitimate tools commonly used by administrators. This demonstrates the use of living off the land tactics (LotL) which are typically hard to detect.
Given the attack’s novelty and LotL techniques, it is no surprise that Darktrace DETECT/Network identified anomalies in usual network behaviour. In particular, Cyber AI Analyst was a large highlight when it came to both Darktrace’s and the security team’s follow-up triage. AI Analyst collated different phases of the compromise such as the network scanning activity, the lateral movement activity over the DCE-RPC protocol, the data exfiltration, and the beaconing activity to the Cobalt Strike endpoints. This helped to map a clear timeline and progression of events along the kill chain.
Figure 1: An AI Analyst Graph showing the timeline of the beaconing activity to the Cobalt Strike Endpoints and the lateral movement activity over the DCE-RPC protocol.
Figure 2: AI Analyst Graph showing the timeline of overall suspicious activities carried out by the compromised devices.
On top of the DETECT product, Darktrace services had a large role to play in the aftermath. The customer subscribed to Darktrace’s Ask the Expert (ATE) service and only became fully aware of the compromise after submitting an ATE ticket requesting assistance investigating one of the related model breaches. Finally, RESPOND itself (although in human confirmation mode) was still able to be used to manually quarantine devices.
Conclusion
During this incident, the initial point of infection, data exfiltration endpoint, and Cobalt Strike C2 Servers were recently created and had no OSINT associating them with malicious activity. This demonstrates how ineffective traditional signature-based intrusion detection systems can be at detecting compromises and how effective Darktrace is at detecting novel campaigns and attacks. Despite this, detection is clearly not enough, especially as out-of-hours attacks increase in frequency and effectiveness. This customer had RESPOND in human confirmation mode which meant that the activity was acted upon and stopped slower than had it been set autonomously. If malicious data loss is to be stopped in full, companies need to reduce reliance on humans and embrace AI-based protection.
Thanks to Darktrace analyst Steve Robinson for his insights on the above threat investigation.
Appendices
Related AI Analyst Incidents
Unusual Repeated Connections
Suspicious DCE-RPC Activity
Internal Download and External Upload
Scanning of Multiple Devices
Possible SSL Command and Control Activity to Multiple Endpoints
Suspicious Remote WMI Activity
Access of Probable Unencrypted Password File
Extensive Suspicious DCE-RPC Activity
Suspicious Remote Control Service Activity
Indicators of Compromise
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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.
Phishing and Persistence: Darktrace’s Role in Defending Against a Sophisticated Account Takeover
The exploitation of SaaS platforms
As businesses continue to grow and evolve, the need for sharing ideas through productivity and cloud Software-as-a-Service (SaaS) platforms is becoming increasingly crucial. However, these platforms have also become prime targets for cyber attackers.
Threat actors often exploit these widely-used services to gain unauthorized access, steal sensitive information, and disrupt business operations. The growing reliance on SaaS platforms makes them attractive entry points for cybercriminals, who use sophisticated techniques such as phishing, social engineering, and malware to compromise these systems.
Services like Microsoft 365 are regularly targeted by threat actors looking for an entry point into an organization’s environment to carry out malicious activities. Securing these platforms is crucial to protect business data and ensure operational continuity.
Darktrace / EMAIL detection of the phishing attack
In a recent case, Darktrace observed a customer in the manufacturing sector receiving a phishing email that led to a threat actor logging in and creating an email rule. Threat actors often create email rules to move emails to their inbox, avoiding detection. Additionally, Darktrace detected a spoofed domain registered by the threat actor. Despite already having access to the customer’s SaaS account, the actor seemingly registered this domain to maintain persistence on the network, allowing them to communicate with the spoofed domain and conduct further malicious activity.
Darktrace / EMAIL can help prevent compromises like this one by blocking suspicious emails as soon as they are identified. Darktrace’s AI-driven email detection and response recognizes anomalies that might indicate phishing attempts and applies mitigative actions autonomously to prevent the escalation of an attack.
Unfortunately, in this case, Darktrace was not configured in Autonomous Response mode at the time of the attack, meaning actions had to be manually applied by the customer’s security team. Had it been fully enabled, it would have held the emails, preventing them from reaching the intended recipient and stopping the attack at its inception.
However, Darktrace’s Managed Threat Detection alerted the Security Operations Center (SOC) team to the compromise, enabling them to thoroughly investigate the incident and notify the customer before further damage could occur.
The Managed Threat Detection service continuously monitors customer networks for suspicious activities that may indicate an emerging threat. When such activities are detected, alerts are sent to Darktrace’s expert Cyber Analysts for triage, significantly speeding up the remediation process.
Attack Overview
On May 2, 2024, Darktrace detected a threat actor targeting a customer in the manufacturing sector then an unusual login to their SaaS environment was observed prior to the creation of a new email rule.
Darktrace immediately identified the login as suspicious due to the rarity of the source IP (31.222.254[.]27) and ASN, coupled with the absence of multi-factor authentication (MFA), which was typically required for this account.
The new email rule was intended to mark emails as read and moved to the ‘Conversation History’ folder for inbound emails from a specific domain. The rule was named “….,,,”, likely the attacker attempting to setup their new rule with an unnoteworthy name to ensure it would not be noticed by the account’s legitimate owner. Likewise, by moving emails from a specific domain to ‘Conversation History’, a folder that is rarely used by most users, any phishing emails sent by that domain would remain undetected by the user.
Figure 1: Darktrace’s detection of the unusual SaaS login and subsequent creation of the new email rule “….,,,”.
The domain in question was identified as being newly registered and an example of a typosquat domain. Typosquatting involves registering new domains with intentional misspelling designed to convince users to visit fake, and often malicious, websites. This technique is often used in phishing campaigns to create a sense of legitimacy and trust and deceive users into providing sensitive information. In this case, the suspicious domain closely resembled several of the customer’s internal domains, indicating an attempt to impersonate the organization’s legitimate internal sites to gain the target’s trust. Furthermore, the creation of this lookalike domain suggests that the attack was highly targeted at this specific customer.
Interestingly, the threat actor registered this spoofed domain despite already having account access. This was likely intended to ensure persistence on the network without having to launch additional phishing attacks. Such use of spoofed domain could allow an attacker to maintain a foothold in their target network and escalate their malicious activities without having to regain access to the account. This persistence can be used for various purposes, including data exfiltration, spreading malware, or launching further attacks.
Following this, Darktrace detected a highly anomalous email being sent to the customer’s account from the same location as the initial unsual SaaS login. Darktrace’s anomaly-based detection is able to identify threats that human security teams and traditional signature-based methods might miss. By analyzing the expected behavior of network users, Darktrace can recognize the subtle deviations from the norm that may indicate malicious activity. Unfortunately, in this instance, without Darktrace’s Autonomous Response capability enabled, the phishing email was able to successfully reach the recipient. While Darktrace / EMAIL did suggest that the email should be held from the recipients inbox, the customer was required to manually approve it.
Despite this, the Darktrace SOC team were still able to support the customer as they were subscribed to the Managed Threat Detection service. Following the detection of the highlight anomalous activity surrounding this compromise, namely the unusual SaaS login followed by a new email rule, an alert was sent to the Darktrace SOC for immediate triage, who then contacted the customer directly urging immediate action.
Conclusion
This case underscores the need to secure SaaS platforms like Microsoft 365 against sophisticated cyber threats. As businesses increasingly rely on these platforms, they become prime targets for attackers seeking unauthorized access and disruption.
Darktrace’s anomaly-based detection and response capabilities are crucial in identifying and mitigating such threats. In this instance, Darktrace detected a phishing email that led to a threat actor logging in and creating a suspicious email rule. The actor also registered a spoofed domain to maintain persistence on the network.
Darktrace / EMAIL, with its AI-driven detection and analysis, can block suspicious emails before they reach the intended recipient, preventing attacks at their inception. Meanwhile, Darktrace’s SOC team promptly investigated the activity and alerted the customer to the compromise, enabling them to take immediate action to remediate the issue and prevent any further damage.
Credit to Vivek Rajan (Cyber Security Analyst) and Ryan Traill (Threat Content Lead).
Lifting the Fog: Darktrace’s Investigation into Fog Ransomware
Introduction to Fog Ransomware
As ransomware attacks continue to be launched at an alarming rate, Darktrace’s Threat Research team has identified that familiar strains like Akira, LockBit, and BlackBasta remain among the most prevalent threats impacting its customers, as reported in the First 6: Half-Year Threat Report 2024. Despite efforts by law agencies, like dismantling the infrastructure of cybercriminals and shutting down their operations [2], these groups continue to adapt and evolve.
As such, it is unsurprising that new ransomware variants are regularly being created and launched to get round law enforcement agencies and increasingly adept security teams. One recent example of this is Fog ransomware.
What is Fog ransomware?
Fog ransomware is strain that first appeared in the wild in early May 2024 and has been observed actively using compromised virtual private network (VPN) credentials to gain access to organization networks in the education sector in the United States.
Darktrace's detection of Fog Ransomware
In June 2024, Darktrace observed instances of Fog ransomware across multiple customer environments. The shortest time observed from initial access to file encryption in these attacks was just 2 hours, underscoring the alarming speed with which these threat actors can achieve their objectives.
Darktrace identified key activities typical of a ransomware kill chain, including enumeration, lateral movement, encryption, and data exfiltration. In most cases, Darktrace was able to successfully halt the progression Fog attacks in their early stages by applying Autonomous Response actions such as quarantining affected devices and blocking suspicious external connections.
To effectively illustrate the typical kill chain of Fog ransomware, this blog focuses on customer environments that did not have Darktrace’s Autonomous Response enabled. In these cases, the attack progressed unchecked and reached its intended objectives until the customer received Darktrace’s alerts and intervened.
Darktrace’s Coverage of Fog Ransomware
Initial Intrusion
After actors had successfully gained initial access into customer networks by exploiting compromised VPN credentials, Darktrace observed a series of suspicious activities, including file shares, enumeration and extensive scanning. In one case, a compromised domain controller was detected making outgoing NTLM authentication attempts to another internal device, which was subsequently used to establish RDP connections to a Windows server running Hyper-V.
Given that the source was a domain controller, the attacker could potentially relay the NTLM hash to obtain a domain admin Kerberos Ticket Granting Ticket (TGT). Additionally, incoming NTLM authentication attempts could be triggered by tools like Responder, and NTLM hashes used to encrypt challenge response authentication could be abused by offline brute-force attacks.
Darktrace also observed the use of a new administrative credential on one affected device, indicating that malicious actors were likely using compromised privileged credentials to conduct relay attacks.
Establish Command-and-Control Communication (C2)
In many instances of Fog ransomware investigated by Darktrace’s Threat Research team, devices were observed making regular connections to the remote access tool AnyDesk. This was exemplified by consistent communication with the endpoint “download[.]anydesk[.]com” via the URI “/AnyDesk.exe”. In other cases, Darktrace identified the use of another remote management tool, namely SplashTop, on customer servers.
In ransomware attacks, threat actors often use such legitimate remote access tools to establish command-and-control (C2) communication. The use of such services not only complicates the identification of malicious activities but also enables attackers to leverage existing infrastructure, rather than having to implement their own.
Internal Reconnaissance
Affected devices were subsequently observed making an unusual number of failed internal connections to other internal locations over ports such as 80 (HTTP), 3389 (RDP), 139 (NetBIOS) and 445 (SMB). This pattern of activity strongly indicated reconnaissance scanning behavior within affected networks. A further investigation into these HTTP connections revealed the URIs “/nice ports”/Trinity.txt.bak”, commonly associated with the use of the Nmap attack and reconnaissance tool.
Simultaneously, some devices were observed engaging in SMB actions targeting the IPC$ share and the named pipe “srvsvc” on internal devices. Such activity aligns with the typical SMB enumeration tactics, whereby attackers query the list of services running on a remote host using a NULL session, a method often employed to gather information on network resources and vulnerabilities.
Lateral Movement
As attackers attempted to move laterally through affected networks, Darktrace observed suspicious RDP activity between infected devices. Multiple RDP connections were established to new clients, using devices as pivots to propagate deeper into the networks, Following this, devices on multiple networks exhibited a high volume of SMB read and write activity, with internal share drive file names being appended with the “.flocked” extension – a clear sign of ransomware encryption. Around the same time, multiple “readme.txt” files were detected being distributed across affected networks, which were later identified as ransom notes.
Further analysis of the ransom note revealed that it contained an introduction to the Fog ransomware group, a summary of the encryption activity that had been carried out, and detailed instructions on how to communicate with the attackers and pay the ransom.
Figure 1: Packet capture (PCAP) of the ransom note file titled “readme.txt”.
Data Exfiltration
In one of the cases of Fog ransomware, Darktrace’s Threat Research team observed potential data exfiltration involving the transfer of internal files to an unusual endpoint associated with the MEGA file storage service, “gfs302n515[.]userstorage[.]mega[.]co[.]nz”.
This exfiltration attempt suggests the use of double extortion tactics, where threat actors not only encrypt victim’s data but also exfiltrate it to threaten public exposure unless a ransom is paid. This often increases pressure on organizations as they face the risk of both data loss and reputational damage caused by the release of sensitive information.
Darktrace’s Cyber AI Analyst autonomously investigated what initially appeared to be unrelated events, linking them together to build a full picture of the Fog ransomware attack for customers’ security teams. Specifically, on affected networks Cyber AI Analyst identified and correlated unusual scanning activities, SMB writes, and file appendages that ultimately suggested file encryption.
Figure 2: Cyber AI Analyst’s analysis of encryption activity on one customer network.
Figure 3: Cyber AI Analysts breakdown of the investigation process between the linked incident events on one customer network.
Safeguarding vulnerable sectors with real-time ransomware mitigation
As novel and fast-moving ransomware variants like Fog persist across the threat landscape, the time taken for from initial compromise to encryption has significantly decreased due to the enhanced skill craft and advanced malware of threat actors. This trend particularly impacts organizations in the education sector, who often have less robust cyber defenses and significant periods of time during which infrastructure is left unmanned, and are therefore more vulnerable to quick-profit attacks.
Traditional security methods may fall short against these sophisticated attacks, where stealthy actors evade detection by human-managed teams and tools. In these scenarios Darktrace’s AI-driven product suite is able to quickly detect and respond to the initial signs of compromise through autonomous analysis of any unusual emerging activity.
When Darktrace’s Autonomous Response capability was active, it swiftly mitigated emerging Fog ransomware threats by quarantining devices exhibiting malicious behavior to contain the attack and blocking the exfiltration of sensitive data, thus preventing customers from falling victim to double extortion attempts.
Darktrace’s First 6: Half-Year Threat Report 2024 highlights the latest attack trends and key threats observed by the Darktrace Threat Research team in the first six months of 2024.
Focuses on anomaly detection and behavioral analysis to identify threats
Maps mitigated cases to known, publicly attributed threats for deeper context
Offers guidance on improving security posture to defend against persistent threats
Appendices
Credit to Qing Hong Kwa (Senior Cyber Analyst and Deputy Analyst Team Lead, Singapore) and Ryan Traill (Threat Content Lead)
Darktrace Model Detections:
- Anomalous Server Activity::Anomalous External Activity from Critical Network Device
- Anomalous Connection::SMB Enumeration
- Anomalous Connection::Suspicious Read Write Ratio and Unusual SMB
- Anomalous Connection::Uncommon 1 GiB Outbound
- Anomalous File::Internal::Additional Extension Appended to SMB File
