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The authorization bypass vulnerability in Chainlit versions prior to 2.8.5 operates through user-controlled keys, specifically in thread management functionalities. When users authenticate, the application generates keys or identifiers for accessing threads, but these keys are inadequately validated server-side. Attackers who can log in may manipulate thread IDs in API requests, such as via parameters in endpoints like /api/threads/{thread_id}, to access threads owned by other users. This occurs because the authorization mechanism trusts user-provided keys without verifying ownership against session data. For instance, an attacker could modify the thread ID in a GET request to retrieve unauthorized conversation data. The vulnerability stems from missing server-side checks that should map thread IDs to authenticated user IDs in the database. By brute-forcing or guessing thread identifiers, an attacker can view sensitive threads or even claim ownership by altering key values in update requests. This bypass is facilitated by insecure direct object references (IDOR) in the codebase, where access control lists are not enforced. The low severity reflects the requirement for attacker login credentials, but it enables privilege escalation within the user context. Fixes in version 2.8.5 likely involve implementing proper authorization middleware that validates each request key against user permissions, ensuring thread ownership before granting access.
Platform: Chainlit
Version: versions < 2.8.5
Vulnerability: Authorization Bypass
Severity: Low
date: Jan 14 2026
Prediction: Jan 14 2026
What Undercode Say:
Showing bash commands and codes related to the blog
– Check version: `chainlit –version`
– Exploit test: `curl -X GET http://localhost:8000/api/threads/12345 -H “Authorization: Bearer
– Python snippet: `requests.get(f”http://localhost:8000/api/threads/{thread_id}”, headers={“Authorization”: “Bearer
how Exploit:
- Login with credentials.
- Manipulate thread ID in requests.
- Access unauthorized threads.
Protection from this CVE
- Upgrade to 2.8.5.
- Implement server-side checks.
- Validate user ownership.
Impact:
- Data leakage.
- Unauthorized access.
- Privilege escalation.
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Sources:
Reported By: github.com
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