BianLian group exploits JetBrains TeamCity bugs in ransomware attacks
Vulnerabilities mentionedAll →
| CVE | Vulnerability | CVSS | EPSS | Flags | Affected | Exposure | Published |
|---|---|---|---|---|---|---|---|
| CVE-2023-42793 | Authentication bypass in JetBrains TeamCity enables unauthenticated RCE JetBrains TeamCity Server, a widely used CI/CD build server, contains an authentication bypass vulnerability (CWE-288) that lets a remote, unauthenticated attacker gain administrative access without valid credentials. By sending crafted requests to the TeamCity server over the network, the attacker bypasses authentication and can then execute arbitrary code on the server via administrative and build features, achieving full remote code execution. An attacker gains control of the build server and, with it, access to source code, build artifacts, stored secrets and credentials, and a foothold for lateral movement or ransomware deployment. Any organization running an affected TeamCity Server is affected, especially instances reachable from the internet. Exploitation is confirmed in the wild: CISA added the flaw to its KEV catalog on 2023-10-04 with known ransomware use, and EPSS assigns a 100% probability of exploitation within 30 days. Do: Upgrade TeamCity Server to 2023.05.4 or later per JetBrains' instructions, or apply vendor mitigations or discontinue use if patching is not possible (per the CISA KEV required action). Also take unpatched instances off the public internet, and hunt for signs of compromise such as unauthorized administrator accounts, unexpected changes in audit logs and build configurations, and stored secrets or tokens that may have been stolen, given known ransomware exploitation. | 9.8 | 100% | KEV ransomware PoC ×2 |
| largeTens of thousands of TeamCity Server deployments, of which several thousand are internet-exposed | |
| CVE-2024-27198 | Authentication Bypass in JetBrains TeamCity CI/CD Server CVE-2024-27198 is an authentication bypass (CWE-288) in JetBrains TeamCity, JetBrains' self-hosted on-premises continuous integration/continuous delivery (CI/CD) server, that allows an unauthenticated attacker to circumvent login and perform administrative actions. It is triggered by sending specially crafted requests to the TeamCity web interface that dodge the authentication check, after which the attacker gains full administrator access. With admin access, an attacker can create administrative accounts, alter build configurations, plant code that runs on the server and its build agents, and reach source code, credentials, and secrets stored in the CI/CD environment, which ransomware operators have already used as an entry point. Any TeamCity deployment an attacker can reach over the network is affected, with internet-facing instances at the highest risk. Exploitation is confirmed in the wild: CISA added the flaw to the KEV catalog on 2024-03-07 with known ransomware use, and EPSS estimates a 99.9% probability of exploitation within 30 days. Do: Upgrade immediately to the patched TeamCity release per JetBrains' advisory (2023.11.4 or later fixes this vulnerability), or apply vendor mitigations or discontinue use per CISA guidance if patching is not possible. Audit instances for unexpected administrator accounts, modified build configurations, and other signs of compromise, since ransomware operators are known to be actively exploiting this bug. Restrict TeamCity's network exposure to trusted users and networks until the update is applied. | 9.8 | 100% | KEV ransomware |
| largetens of thousands of internet-exposed TeamCity servers (roughly 20,000–30,000 per public scans at disclosure) |
Indicators of compromiseauto-extracted · verify before use · export allAll →
| Type | Indicator | Context |
|---|---|---|
| ipv4 | 136.0.3.71 | ’ is converted into decimal notation, the observed value is 136.0.3.71 which is an IP address linked to a server that hosted the B |
Full article382 words · extracted from securityaffairs.com · click to collapse
BianLian ransomware group was spotted exploiting vulnerabilities in JetBrains TeamCity software in recent attacks.
Researchers from GuidePoint Security noticed, while investigating a recent attack linked to the BianLian ransomware group, that the threat actors gained initial access to the target by exploiting flaws in a TeamCity server.
The BianLian ransomware emerged in August 2022, the malware was employed in attacks against organizations in various industries, including manufacturing, media and entertainment, and healthcare.
In January 2023, security firm Avast released a free decryptor for the BianLian ransomware to allow victims of the malware to recover locked files.
The threat actors behind the attack investigated by the researchers exploited TeamCity flaws CVE-2024-27198 or CVE-2023-42793 to gain initial access to the victim’s environment. The attackers created new users on the vulnerable server and executed malicious commands for post-exploitation and lateral movement.
Then the threat actor discovered two build servers in the target environment from which they expanded their foothold in the victim organization and pivoted for further exploitation.
The researchers noticed that the BianLian group failed multiple attempts to execute their custom GO backdoor, then pivoted to living off the land and leveraged a PowerShell implementation of their backdoor.
The PowerShell backdoor was obfuscated but didn’t employ any novel techniques to evade detection or prevent the malware from being analyzed.
GuidePoint Security analyzed the PowerShell script and noticed the use of the function ‘cookies’ with specific parameters.
Upon passing the hexadecimal value in ‘Cookies_Param1’ is converted into decimal notation, the observed value is 136.0.3.71 which is an IP address linked to a server that hosted the BianLian GO backdoor as of March 6th, 2024.
GuidePoint also observed several detections for the Microsoft AV signature Win64/BianDoor.D shortly before the first successful execution of the PowerShell backdoor.
“As we have seen throughout 2023 and into 2024, BianLian continues to prove how they can adapt to a changing environment, especially in regards to the exploitation of emerging vulnerabilities. This behavior aligns with what GRIT has assessed and hypothesized in our 2024 ransomware report, and we expect this type of behavior to continue to grow, especially for groups that leverage a data-exfiltration-only approach to ransomware.” reads the report published by GuidePoint Security.
Follow me on Twitter: @securityaffairs and Facebook and Mastodon
(SecurityAffairs – hacking, JetBrains TeamCity)
Text extracted automatically; images, tables and formatting may be missing. Original: https://securityaffairs.com/160357/hacking/bianlian-group-ttack-jetbrains-teamcity.html