2026-07-02 · 2026-Q3
fast-mcp-telegram MCP Server Authentication Bypass (CVE-2026-52830)
Which agent, run, or tenant is this?
- Fixable
- Vendor patch
- Vendor response
- Patched
- In the wild
- No
- Actor
- Attacker
Target
fast-mcp-telegram MCP server (PyPI), versions before 0.19.1
Impact
A remote, unauthenticated attacker bypasses authentication with a crafted Bearer token such as `../fast-mcp-telegram/telegram` to authenticate as the default legacy session, reaching the MCP tools and the connected Telegram account data across tenant boundaries
Root cause
The Bearer token is joined directly into a session-file path with no normalization; the server rejects the literal token "telegram" but not path separators (CWE-22 path traversal plus CWE-287 improper authentication)
CVE
Sources
Catalog
Cite this: AgentProv incident record: fast-mcp-telegram MCP Server Authentication Bypass (CVE-2026-52830) (2026-07-02). https://agentprov.com/incidents/2026-07-02-fast-mcp-telegram-mcp-server-authentication-bypass-cve-2026-52830
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