https://vulnerability.circl.lu/rss/recent/all/10 Most recent entries from all 2026-10-09T20:08:04.473502+00:00 Vulnerability-Lookup info@circl.lu python-feedgen Contains only the most 10 recent entries. https://vulnerability.circl.lu/vuln/cve-2026-52830 CVE-2026-52830 — fast-mcp-telegram: Bearer token path traversal bypasses reserved Telegram session protection 2026-10-09T20:08:05.632742+00:00

Affected: leshchenko1979 fast-mcp-telegram

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.

 https://vulnerability.circl.lu/vuln/pysec-2026-2473 PYSEC-2026-2473 — fast-mcp-telegram: Bearer token path traversal bypasses reserved Telegram session protection 2026-10-09T20:08:05.632853+00:00

Affected: PyPI: fast-mcp-telegram

## Summary

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 bearer token, if that legacy or default session file is present on a server running HTTP auth. The attacker can then call Telegram MCP tools as that account, including message reading, message sending, MTProto API calls, and attachment-producing tool surfaces available to the session.

## Technical details

`SessionFileTokenVerifier.verify_token()` strips whitespace and rejects exact reserved names:

```python if token.lower() in RESERVED_SESSION_NAMES: return None ```

It t…