EUVD-2026-42913
GHSA-ch3x-q6cp-54rw
Severity by source
AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
Unauthenticated network injection (PR:N/AV:N) but fires only when a victim views the page (UI:R); stored XSS executes in the victim's browser context, so S:C with limited C/I and no availability impact.
Primary rating from Vendor (JetBrains).
CVSS VectorNVD
Lifecycle Timeline
5DescriptionNVD
In JetBrains TeamCity before 2026.1.2 stored XSS via unauthenticated agent registration was possible
AnalysisAI
Stored cross-site scripting in JetBrains TeamCity before 2026.1.2 lets an unauthenticated attacker persist malicious script through the agent registration flow, which then executes in the browser of any privileged user (e.g. an administrator) who later views the affected agent-management interface. Because agent registration requires no authentication, the entry barrier is minimal, and successful execution in an admin session can lead to session/token theft and pivoting to control of a CI/CD build server. No public exploit identified at time of analysis, and the issue is not listed in CISA KEV; EPSS data was not provided.
Technical ContextAI
TeamCity is a widely used CI/CD build-management server; build agents connect to the central server and are enumerated in its web UI. The root cause is CWE-79 (improper neutralization of input during web page generation): attacker-controlled data supplied during the unauthenticated agent registration process is stored server-side and later rendered without adequate output encoding, so it is interpreted as active HTML/JavaScript when a user loads the relevant page. The affected component is the TeamCity server web application (CPE cpe:2.3:a:jetbrains:teamcity), specifically the agent-registration handling and the UI surfaces that display agent-provided metadata.
RemediationAI
Vendor-released patch: 2026.1.2 - upgrade the TeamCity server to 2026.1.2 or later, which is the primary and authoritative fix; consult the JetBrains security bulletin at https://www.jetbrains.com/privacy-security/issues-fixed/ for release specifics. Until the upgrade can be applied, reduce exposure by restricting network access to the TeamCity server and, in particular, to the agent-registration endpoints so that only trusted networks/hosts can register agents (trade-off: legitimate agents on untrusted networks will fail to connect and may need allowlisting or VPN routing). Additionally, advise administrators to avoid browsing agent-management pages from sessions with elevated privileges until patched, and consider a strict Content-Security-Policy at any fronting reverse proxy to limit inline script execution (trade-off: a restrictive CSP can break parts of the TeamCity UI and should be tested first). Do not rely on these as permanent controls - patching is the only complete remediation.
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In JetBrains TeamCity before 2023.05 bypass of permission checks allowing to perform admin actions was possible. Rated c
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Same weakness CWE-79 – Cross-site Scripting (XSS)
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External POC / Exploit Code
Leaving vuln.today