fast-mcp-telegram: Bearer token path traversal bypasses reserved Telegram session protection

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Summary

CVECVE-2026-52830
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-07-02 21:16:56 UTC
Updated2026-07-02 21:16:56 UTC
Descriptionfast-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.

Risk And Classification

Primary CVSS: v3.1 9.4 CRITICAL from [email protected]

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:L

Problem Types: CWE-22 | CWE-287 | CWE-22 CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal') | CWE-287 CWE-287: Improper Authentication

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary9.4CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:L
3.1CNADECLARED9.4CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:L

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
Low

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:L

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Leshchenko1979 Fast-mcp-telegram affected < 0.19.1 Not specified

References

ReferenceSourceLinkTags
web.archive.org/web/20250926152207/https://github.com/leshchenko1979/fast-mcp... [email protected] web.archive.org
github.com/advisories/GHSA-rxw2-pc8j-vxwm [email protected] github.com
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