Vulnerability Description
fast-mcp-telegram is a Telegram MCP Server. Prior to 0.19.1, fast-mcp-telegram validates HTTP Bearer tokens by joining the raw token string into a session-file path. The verifier rejects the exact reserved token telegram, but it does not reject path separators or normalize the path before checking whether the session file exists. A remote HTTP client can therefore authenticate as the default legacy session with a token such as ../fast-mcp-telegram/telegram when the documented default session file ~/.config/fast-mcp-telegram/telegram.session exists. This bypasses the reserved session name control that is intended to prevent HTTP multi-user sessions from colliding with the default stdio or legacy account. With account-prefixed MCP tools enabled, the attacker still sees and calls the prefixed tools for the default account, so the prefix middleware does not stop the session selection bypass. This vulnerability is fixed in 0.19.1.
CVSS Score
CRITICAL
Related Weaknesses (CWE)
References
- https://github.com/advisories/GHSA-rxw2-pc8j-vxwm
- https://web.archive.org/web/20250926152207/https://github.com/leshchenko1979/fas
- https://github.com/advisories/GHSA-rxw2-pc8j-vxwm
FAQ
What is CVE-2026-52830?
CVE-2026-52830 is a vulnerability with a CVSS score of 9.4 (CRITICAL). fast-mcp-telegram is a Telegram MCP Server. Prior to 0.19.1, fast-mcp-telegram validates HTTP Bearer tokens by joining the raw token string into a session-file path. The verifier rejects the exact res...
How severe is CVE-2026-52830?
CVE-2026-52830 has been rated CRITICAL with a CVSS base score of 9.4/10. This is considered a critical vulnerability requiring immediate attention.
Is there a patch for CVE-2026-52830?
Check the references section above for vendor advisories and patch information. Review vendor security bulletins for remediation guidance.