CVE-2026-59791 JetBrains CVE debrief

Who should care

Users of JetBrains YouTrack before version 2026.2.17012 should apply the patch to prevent potential CSS injection attacks. This includes administrators and security teams responsible for maintaining and securing instances of YouTrack. Additionally, developers and operators who work with Mermaid diagrams in YouTrack should be aware of this vulnerability and take necessary precautions.

Technical summary

The vulnerability, CVE-2026-59791, is a CSS injection issue in JetBrains YouTrack before version 2026.2.17012. It occurs via Mermaid diagram rendering. The Common Vulnerability Scoring System (CVSS) score is 3.5, indicating a low severity. The CVSS vector is CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:N/I:L/A:N. This issue can be mitigated by applying the patch to upgrade to version 2026.2.17012 or later.

Defensive priority

Low priority, but recommended to patch for defense-in-depth.

Recommended defensive actions

• Apply the patch to upgrade JetBrains YouTrack to version 2026.2.17012 or later.
• Review and monitor Mermaid diagram rendering in YouTrack for suspicious activity.
• Consider implementing additional security measures for YouTrack, such as input validation and content security policy.
• Review compensating controls for exposed systems while remediation is scheduled and verified.
• Check relevant monitoring, detection, and logs for exposed assets that need extra review.

Evidence notes

The CVE record and NVD entry provide limited information about the vulnerability. Further investigation and verification are recommended. The vulnerability allows for CSS injection via Mermaid diagram rendering in JetBrains YouTrack before version 2026.2.17012. Users should verify their deployments and apply patches accordingly. Evidence is limited, and defenders should review the official advisory for affected scope and severity.

Official resources