Authenticated chat interruption via missing ownership check
Published May 8, 2026 · Updated May 8, 2026
Authorization bypass in Onyx before 3.0.9, 3.1.0 through 3.1.5, and 3.2.0 through 3.2.5 allows remote authenticated users to interrupt chats. The stop_chat_session endpoint accepts a caller-controlled chat_session_id and sets its cache fence without checking that the authenticated user owns the session. Knowledge of another active session UUID is required, and repeated requests terminate that user’s LLM generations mid-stream without exposing or modifying stored chat data.
Summary
What happened
Authorization bypass in Onyx before 3.0.9, 3.1.0 through 3.1.5, and 3.2.0 through 3.2.5 allows remote authenticated users to interrupt chats. The stop_chat_session endpoint accepts a caller-controlled chat_session_id and sets its cache fence without checking that the authenticated user owns the session. Knowledge of another active session UUID is required, and repeated requests terminate that user’s LLM generations mid-stream without exposing or modifying stored chat data.
The record
- CVE
- CVE-2026-42276
- Published
- May 8, 2026
- Updated
- May 8, 2026
- Vendor
- Onyx
- Product
- Onyx
- Classifications
- CWE-639, T1499
- Attack vector
- network
- Privileges
- authenticated
Timeline
How it unfolded
- May 8, 2026CVE publishedPublication date reported by the CVE source.
- May 8, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=< 3.0.9
- Affected versionversion=>= 3.1.0, < 3.1.6
- Affected versionversion=>= 3.2.0, < 3.2.6
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
- Two-user stop-chat-session HTTP proof of conceptproof of concept · demonstrated
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Technologies
Your stack
See the directory against your own environment.
Your stack
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