CVE-2026-52830: fast-mcp-telegram: Bearer token path traversal bypasses reserved Telegram session protection
(updated )
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.
References
- github.com/advisories/GHSA-rxw2-pc8j-vxwm
- github.com/leshchenko1979/fast-mcp-telegram/security/advisories/GHSA-rxw2-pc8j-vxwm
- github.com/pypa/advisory-database/tree/main/vulns/fast-mcp-telegram/PYSEC-2026-2473.yaml
- nvd.nist.gov/vuln/detail/CVE-2026-52830
- pypi.org/project/fast-mcp-telegram
- web.archive.org/web/20250926152207/https://github.com/leshchenko1979/fast-mcp-telegram
Code Behaviors & Features
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