CVE-2026-103489 in YouTrack
Summary
by MITRE • 10/01/2026
In JetBrains YouTrack before 2026.2.19422 hTML injection in VCS command failure notifications was possible
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Analysis
by VulDB Data Team • 10/01/2026
The vulnerability identified as HTML injection within JetBrains YouTrack prior to version 2026.2.19422 represents a significant security flaw affecting the integrity and confidentiality of project management data. This issue specifically manifests during the processing of Version Control System commands, particularly when those commands fail to execute successfully. The core technical deficiency lies in how the application handles error messages generated by external VCS integrations such as Git or SVN. Instead of sanitizing or escaping user-supplied input that originates from these failure notifications, YouTrack renders the raw content directly into the web interface. This lack of proper output encoding allows an attacker who can influence the outcome of a VCS operation to inject arbitrary HTML and potentially JavaScript code into the application's response stream.
From a technical perspective, this flaw is classified under CWE-79, which denotes Improper Neutralization of Input During Web Page Generation commonly known as Cross-Site Scripting. The vulnerability operates through a stored or reflected vector depending on how the VCS integration logs errors. If an attacker can manipulate repository metadata, commit messages, or hook scripts to trigger specific failure states in YouTrack's notification system, they can embed malicious payloads within those error reports. When other users view these notifications within their browsers, the injected code executes with the privileges of the authenticated session. This mechanism bypasses standard security controls because the content is treated as trusted by the browser due to its origin from a legitimate domain served by YouTrack.
The operational impact of this vulnerability extends beyond simple defacement or cosmetic issues. Successful exploitation can lead to Session Hijacking, where an attacker steals authentication cookies and gains unauthorized access to victim accounts. It also enables Phishing attacks, where malicious forms are injected into the interface to harvest credentials for other systems connected via Single Sign-On protocols. Furthermore, attackers could perform actions on behalf of victims if they have sufficient permissions within YouTrack, such as modifying issues, changing workflow states, or accessing sensitive project documentation. The risk is amplified in environments where multiple teams collaborate, as a single compromised notification can affect numerous users across different projects without their knowledge.
Mitigation strategies must prioritize immediate patching and defensive configuration adjustments. Organizations running affected versions of JetBrains YouTrack should upgrade to version 2026.2.19422 or later, which includes the necessary code changes to properly sanitize input from VCS failure notifications. Until patches are applied, administrators can implement Web Application Firewall rules that detect and block common HTML injection patterns in request parameters related to VCS integrations. Additionally, enabling Content Security Policy headers with strict directives regarding script execution can mitigate the impact of any successfully injected scripts by preventing them from executing unless they originate from explicitly trusted sources. Regular audits of third-party plugin configurations and VCS hook scripts are also recommended to ensure that no malicious payloads are being introduced at the source before reaching the YouTrack application layer.
This vulnerability aligns with MITRE ATT&CK technique T1059, Command and Scripting Interpreter, specifically when used for client-side script execution via browser-based interfaces. It highlights the critical importance of secure coding practices in enterprise software that integrates with external systems. Developers must ensure that all data originating from untrusted sources, including error messages from integrated tools like Git or SVN, undergo rigorous validation and encoding before being rendered to end-users. The resolution underscores the need for continuous security monitoring and prompt application of vendor updates to maintain a robust defense posture against web-based injection attacks.