CVE-2026-52830 Details
Description
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.
A path traversal vulnerability has been identified in fast-mcp-telegram, a Telegram MCP server, in versions prior to 0.19.1. The issue arises because the application validates HTTP Bearer tokens by concatenating the raw token into a session file path without properly normalizing it or rejecting path separators. This allows a remote HTTP client to authenticate as the default legacy session by using a crafted token that exploits the path traversal, bypassing intended session name controls. As a result, an attacker can access the default Telegram account's MCP tools, including message reading and sending capabilities.
Users are advised to update fast-mcp-telegram to version 0.19.1 or later, and to implement strict validation for Bearer tokens before using them in file paths. This includes rejecting path traversal characters and ensuring tokens are opaque identifiers.
Metrics
CVSS 4.0 Severity and Vector Strings:
VolerionCVSS 3.x Severity and Vector Strings:
No data available for CVSS Version 2.0 on this CVE.
Volerion
Assessed Jul 2, 2026CISA-ADP
Assessed Jul 6, 2026References to Advisories, Solutions, and Tools
By selecting these links, you will be leaving this site. These are references gathered from the official CVE record and are not endorsed by Volerion.
| URL | Source(s) | Tag(s) |
|---|---|---|
| https://github.com/advisories/GHSA-rxw2-pc8j-vxwm | CISA-ADP | AdvisoryExploitRemedyVendor |
| https://github.com/advisories/GHSA-rxw2-pc8j-vxwm | [email protected] | AdvisoryExploitRemedyVendor |
| https://web.archive.org/web/20250926152207/https://github.com/leshchenko1979/fast-mcp-telegram | [email protected] | ProductSource CodeVendor |
Weakness Enumeration
| CWE-ID | CWE Name | Source |
|---|---|---|
| CWE-22 | Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal') | [email protected] |
| CWE-287 | Improper Authentication | [email protected] |
Affected Products
| Product | Versions |
|---|---|
| fast-mcp-telegram | <= 0.19.0 (semver) |
CPE
Remediation
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Change History
2 change records found show changes
| Date | Action | Recorded By |
|---|---|---|
| Jul 6, 2026 | CVE Modified | CISA-ADP |
| Jul 2, 2026 | New CVE Received | [email protected] |