BianLian Threat Actors Exploiting JetBrains TeamCity Flaws in Ransomware Attacks
Vulnerabilities mentionedAll →
| CVE | Vulnerability | CVSS | EPSS | Flags | Affected | Exposure | Published |
|---|---|---|---|---|---|---|---|
| CVE-2023-22527 | Unauthenticated OGNL Template Injection RCE in Atlassian Confluence Data Center/Server Atlassian Confluence Data Center and Server contain an unauthenticated OGNL template injection vulnerability (CWE-74) in which attacker-controlled input is evaluated by the application as an OGNL expression. A remote, unauthenticated attacker can trigger the flaw by sending a crafted HTTP request that injects OGNL expressions, which the server then executes. Successful exploitation leads to remote code execution on the host running Confluence, giving the attacker control of the system without any credentials. Any organization running self-hosted Confluence Data Center or Server is potentially affected — the available data does not specify version ranges, so operators should consult Atlassian's advisory — with internet-facing instances at highest risk. Exploitation is active: the flaw was added to CISA's Known Exploited Vulnerabilities catalog on 2024-01-24 with known ransomware use, and EPSS assigns it a 100% probability of exploitation within 30 days (100th percentile). Do: Patch to the fixed release specified in Atlassian's advisory immediately, prioritizing internet-exposed instances, since the flaw is in CISA's KEV with known ransomware use and carries a 100% EPSS. If patching is not immediately possible, apply the vendor's mitigations per the KEV required action — or discontinue/restrict use — for example by limiting unauthenticated access to Confluence from the internet. Review Confluence access and application logs for anomalous unauthenticated requests and indicators of command execution or ransomware activity. | 9.8 | 100% | KEV ransomware PoC ×2 |
| largetens of thousands of internet-exposed Confluence instances (order of 10,000–100,000) | |
| 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) |
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Ravie LakshmananMar 11, 2024Ransomware / Vulnerability
The threat actors behind the BianLian ransomware have been observed exploiting security flaws in JetBrains TeamCity software to conduct their extortion-only attacks.
According to a new report from GuidePoint Security, which responded to a recent intrusion, the incident "began with the exploitation of a TeamCity server which resulted in the deployment of a PowerShell implementation of BianLian's Go backdoor."
BianLian emerged in June 2022, and has since pivoted exclusively to exfiltration-based extortion following the release of a decryptor in January 2023.
The attack chain observed by the cybersecurity firm entails the exploitation of a vulnerable TeamCity instance using CVE-2024-27198 or CVE-2023-42793 to gain initial access to the environment, followed by creating new users in the build server and executing malicious commands for post-exploitation and lateral movement.
It's currently not clear which of the two flaws were weaponized by the threat actor for infiltration.
BianLian actors are known to implant a custom backdoor tailored to each victim written in Go, as well as drop remote desktop tools like AnyDesk, Atera, SplashTop, and TeamViewer. The backdoor is tracked by Microsoft as BianDoor.
“BianLian's backdoor, similar to the encryptor, is written in Go. Its core functionality is more of a loader than a classic backdoor, with its main functionality being downloading and executing additional payloads,” Palo Alto Networks Unit 42 noted in January 2024. “The backdoor contains a hard-coded C2 IP address and port to communicate with.”
"After multiple failed attempts to execute their standard Go backdoor, the threat actor pivoted to living-off-the-land and leveraged a PowerShell implementation of their backdoor, which provides an almost identical functionality to what they would have with their Go backdoor," security researchers Justin Timothy, Gabe Renfro, and Keven Murphy said.
The obfuscated PowerShell backdoor ("web.ps1") is designed to establish a TCP socket for additional network communication to an actor-controlled server, allowing the remote attackers to conduct arbitrary actions on an infected host.
"The now-confirmed backdoor is able to communicate with the [command-and-control] server and asynchronously execute based on the remote attacker's post-exploitation objectives," the researchers said.
The disclosure comes as VulnCheck detailed fresh proof-of-concept (PoC) exploits for a critical security flaw impacting Atlassian Confluence Data Center and Confluence Server (CVE-2023-22527) that could lead to remote code execution in a fileless manner and load the Godzilla web shell directly into memory.
The flaw has since been weaponized to deploy C3RB3R ransomware, cryptocurrency miners and remote access trojans over the past two months, indicating widespread exploitation in the wild.
"There's more than one way to reach Rome," VulnCheck's Jacob Baines noted. "While using freemarker.template.utility.Execute appears to be the popular way of exploiting CVE-2023-22527, other more stealthy paths generate different indicators."
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