Critical, CVSS 9.4PyPIAmendedPublished
fast-mcp-telegram: Bearer token path traversal bypasses reserved Telegram session protection
CVE-2026-52830 · GHSA-rxw2-pc8j-vxwm
- Affected
- PyPI fast-mcp-telegram <= 0.19.0
- Fixed in
- 0.19.1· Vendor fix available
- Issue
- 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. Impact An unauthenticated network client can access the Telegram account represented by the default telegram.session file without knowing a generated…
Recommended action: Upgrade to 0.19.1 or later, then redeploy and verify.A vendor fix does not resolve your finding until you verify it in your own systems.