Critical TeamCity Flaw Could Let Attackers Run OS Commands Without Logging In
Vulnerabilities mentionedAll →
| CVE | Vulnerability | CVSS | EPSS | Flags | Affected | Exposure | Published |
|---|---|---|---|---|---|---|---|
| CVE-2026-63077 | Unauthenticated Deserialization RCE in JetBrains TeamCity On-Premises CVE-2026-63077 is a critical (CVSS 9.8) unauthenticated remote code execution vulnerability in JetBrains TeamCity, caused by deserialization of untrusted data (CWE-502) in the agent polling protocol. An attacker with network access to the TeamCity server, but no credentials of any kind, can send maliciously crafted serialized input to the agent polling endpoint and execute arbitrary code on the server. Successful exploitation yields full server takeover, exposing source code, build logs, stored secrets and credentials, and providing a pivot point into build agents and connected infrastructure; related headlines describe a real breach in which AWS credentials were extracted from an unpatched TeamCity instance. Organizations running TeamCity On-Premises in versions prior to the fixes (2025.11.7 or 2026.1.3, depending on branch) are affected, while the JetBrains-hosted cloud service is not indicated as impacted. Exploitation is confirmed in the wild: CISA added the flaw to the Known Exploited Vulnerabilities catalog on 2026-08-05, EPSS is 86.5% (100th percentile), and no public PoC is known, meaning defenders cannot rely on public scanners alone and should assume sophisticated attackers are targeting exposed servers. Do: Upgrade immediately to TeamCity 2025.11.7 or 2026.1.3, whichever branch you run; because the flaw is pre-authentication, also hunt for signs of compromise (unexpected builds or agents, new or modified admin users, altered build configurations, and leaked stored credentials/secrets) per vendor guidance, and restrict internet exposure of the TeamCity server until patched. Federal agencies must apply vendor mitigations or discontinue use per CISA BOD 26-04 and the KEV required action, including the Forensics Triage Requirements. | 9.8 | 87% | KEV |
| largetens of thousands of internet-exposed TeamCity on-premises servers (order of magnitude 10k-100k); total on-premises installs likely higher |
Full article316 words · extracted from thehackernews.com · click to collapse
Ravie LakshmananJul 28, 2026Vulnerability / Enterprise Security
JetBrains is urging customers of on-premise versions of TeamCity to update to the latest version following the discovery of a critical security issue that could result in arbitrary code execution.
The vulnerability, assigned CVE-2026-63077 (CVSS score: 9.8), affects all TeamCity On-Premises versions. It has been addressed in versions 2025.11.7 and 2026.1.3. TeamCity Cloud instances have already been updated. JetBrains has credited Antoni Tremblay with discovering and reporting the flaw on July 10, 2026.
"If exploited, this flaw may enable an unauthenticated attacker with HTTP(S) access to a TeamCity server to bypass authentication checks and execute arbitrary operating system commands with the privileges of the TeamCity server process," JetBrains said.
The flaw allows unauthenticated remote code execution via the agent polling protocol to sidestep authentication checks and achieve command execution. Depending on the privileges granted to the TeamCity server process, a successful compromise can lead to the exposure of TeamCity data, configurations, and stored credentials, or modification of server state.
Besides releasing versions 2025.11.7 and 2026.1.3, JetBrains has released a security patch plugin for versions 2017.1+ so that customers who are unable to apply an update can still patch their environments. There is no evidence to indicate that the flaw has been exploited in the wild.
"The security patch plugin will address only the vulnerability described above (CVE-2026-63077)," JetBrains cautioned. "We always recommend upgrading your server to the latest version to benefit from many other security updates."
As best practices, customers are advised to consider requiring VPN connections or implementing an extra layer of security to prevent unauthorized access to internet-facing TeamCity servers.
"Even exposing the TeamCity login screen or REST API can provide attackers with potential entry points to exploit newly disclosed vulnerabilities," it added.
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