leshchenko1979 fast-mcp-telegram up to 0.19.0 Bearer Token path traversal

Summaryinfo

A vulnerability was found in leshchenko1979 fast-mcp-telegram up to 0.19.0. It has been declared as critical. Affected by this vulnerability is an unknown functionality of the file /fast-mcp-telegram/telegram of the component Bearer Token Handler. Such manipulation leads to path traversal. This vulnerability is documented as CVE-2026-52830. The attack can be executed remotely. There is not any exploit available. It is recommended to upgrade the affected component.

Detailsinfo

A vulnerability was found in leshchenko1979 fast-mcp-telegram up to 0.19.0. It has been rated as critical. Affected by this issue is some unknown processing of the file /fast-mcp-telegram/telegram of the component Bearer Token Handler. The manipulation with an unknown input leads to a path traversal vulnerability. Using CWE to declare the problem leads to CWE-22. The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory. Impacted is confidentiality, integrity, and availability. CVE summarizes:

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.

The advisory is available at web.archive.org. This vulnerability is handled as CVE-2026-52830 since 06/08/2026. The exploitation is known to be easy. The attack may be launched remotely. No form of authentication is required for exploitation. Technical details are known, but there is no available exploit. This vulnerability is assigned to T1006 by the MITRE ATT&CK project.

Upgrading to version 0.19.1 eliminates this vulnerability.

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Productinfo

Type

• Artificial Intelligence Software

Vendor

• leshchenko1979

Name

• fast-mcp-telegram

Version

• 0.1
• 0.2
• 0.3
• 0.4
• 0.5
• 0.6
• 0.7
• 0.8
• 0.9
• 0.10
• 0.11
• 0.12
• 0.13
• 0.14
• 0.15
• 0.16
• 0.17
• 0.18
• 0.19.0

CPE 2.3info

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CPE 2.2info

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