JetBrains TeamCity EUVD-2026-42913

Exploitation requires that the TeamCity server's agent registration is reachable by the attacker and accepts registrations without authentication (PR:N), which is the default agent-connection model; the attacker injects the stored payload during that registration. The exploit is LIMITED by required user interaction (UI:R): the injected script only fires when a privileged user - typically an administrator - views the agent-management UI where the attacker-controlled data is rendered. There is no automatic/unattended trigger, so an idle or unviewed malicious agent yields no impact until a victim loads the affected page; impact is further bounded to whatever the victim's browser session is authorized to do.

The CVSS 3.1 base score is 8.1 (AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N), reflecting network reachability, low complexity, and no privileges required, offset only by required user interaction (a privileged user must view the poisoned content). The vendor-supplied vector rates confidentiality and integrity as High with no scope change, which is aggressive for a stored XSS - most stored XSS carries a scope change (script runs in the victim's browser context) with lower per-metric impact; this discrepancy is worth verifying with JetBrains. Countervailing signals: no KEV listing and no known public POC, and no EPSS score was provided, so there is no evidence of active or automatable mass exploitation. The realistic priority is moderate-to-high for TeamCity operators - it is unauthenticated and targets high-value CI/CD admins - but it is gated by user interaction and there is currently no indication of in-the-wild use.

An attacker with only network access to the TeamCity server registers a malicious build agent, embedding a JavaScript payload in an agent-controlled field that is stored by the server. When an administrator later opens the agent list or agent details page, the payload executes in their authenticated session, allowing the attacker to steal session cookies/CSRF tokens or issue actions as that admin - potentially leading to takeover of the CI/CD pipeline. No public POC is known, but the low attack complexity and lack of required authentication make the delivery step straightforward.