CVE-2026-42276: Onyx: IDOR in /chat/stop-chat-session allows any authenticated user to interrupt other users chat sessions

Severity: medium (CVSS 4.3 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2026-05-08 · updated 2026-06-17
Weakness: CWE-639

Description

Onyx is an open-source AI platform. Prior to versions 3.0.9, 3.1.6, and 3.2.6, the POST /chat/stop-chat-session/{chat_session_id} endpoint lets any authenticated user stop any other user's active chat session. The endpoint checks authentication but never verifies the session belongs to the caller. An attacker who knows a chat session UUID can kill another user's LLM generation mid-stream. This issue has been patched in versions 3.0.9, 3.1.6, and 3.2.6.

Affected products

onyx-dot-app onyx: before 3.0.9; from 3.1.0 before 3.1.6; from 3.2.0 before 3.2.6 — fixed in 3.0.9, 3.1.6, 3.2.6

How to fix

Upgrade to a fixed version: onyx-dot-app onyx 3.0.9, 3.1.6, 3.2.6. Check the vendor advisory for mitigations.

References

Get alerted when CVE-2026-42276 or the next vulnerability affects your stack