JetBrains TeamCity vulnerability allows privilege escalation, API exposure (CVE-2026-44413)

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.

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.

In JetBrains TeamCity before 2026.1 2025.11.5 authenticated users could expose server API to unauthorised access