CVE-2026-52830: CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal') in 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.
AI Analysis
Technical Summary
The vulnerability in fast-mcp-telegram (CVE-2026-52830) involves improper limitation of a pathname to a restricted directory (CWE-22). Before version 0.19.1, the software validates HTTP Bearer tokens by concatenating the raw token into a session file path without normalizing or sanitizing path separators. Although the exact reserved token 'telegram' is rejected, tokens containing path traversal sequences (e.g., '../fast-mcp-telegram/telegram') can be used to authenticate as the default legacy session if the corresponding session file exists. This bypasses the intended control preventing session collisions between multi-user HTTP sessions and the default or legacy account. The vulnerability is resolved in version 0.19.1.
Potential Impact
An unauthenticated remote attacker can exploit this vulnerability to bypass session token restrictions and authenticate as the default legacy session user. This leads to unauthorized access with high confidentiality and integrity impact, and a low impact on availability. The attacker can access and invoke prefixed MCP tools for the default account, potentially compromising sensitive operations.
Mitigation Recommendations
This vulnerability is fixed in fast-mcp-telegram version 0.19.1. Users should upgrade to version 0.19.1 or later to remediate this issue. No other mitigation or temporary workaround is documented.
CVE-2026-52830: CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal') in leshchenko1979 fast-mcp-telegram
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.
CVSS v3.1
Score 9.4critical
Affected software
pkg:github/leshchenko1979/fast-mcp-telegramRun on your own infrastructure? Check whether these packages are installed with threat-finder — our free open-source scanner.
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
The vulnerability in fast-mcp-telegram (CVE-2026-52830) involves improper limitation of a pathname to a restricted directory (CWE-22). Before version 0.19.1, the software validates HTTP Bearer tokens by concatenating the raw token into a session file path without normalizing or sanitizing path separators. Although the exact reserved token 'telegram' is rejected, tokens containing path traversal sequences (e.g., '../fast-mcp-telegram/telegram') can be used to authenticate as the default legacy session if the corresponding session file exists. This bypasses the intended control preventing session collisions between multi-user HTTP sessions and the default or legacy account. The vulnerability is resolved in version 0.19.1.
Potential Impact
An unauthenticated remote attacker can exploit this vulnerability to bypass session token restrictions and authenticate as the default legacy session user. This leads to unauthorized access with high confidentiality and integrity impact, and a low impact on availability. The attacker can access and invoke prefixed MCP tools for the default account, potentially compromising sensitive operations.
Mitigation Recommendations
This vulnerability is fixed in fast-mcp-telegram version 0.19.1. Users should upgrade to version 0.19.1 or later to remediate this issue. No other mitigation or temporary workaround is documented.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- GitHub_M
- Date Reserved
- 2026-06-08T18:11:06.662Z
- Cvss Version
- 3.1
- State
- PUBLISHED
- Remediation Level
- null
Threat ID: 6a46d2df27e9c797191734e5
Added to database: 07/02/2026, 21:06:39 UTC
Last enriched: 07/10/2026, 08:49:37 UTC
Last updated: 08/16/2026, 00:41:14 UTC
Views: 95
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