CVE-2026-52830 json
fast-mcp-telegram: Bearer token path traversal bypasses reserved Telegram session protection
published 2026-07-02 4 mo ago modified 2026-10-25 14 d ago also GHSA-rxw2-pc8j-vxwm , PYSEC-2026-2473 , EUVD-2026-41438
- cvss
- 9.4
- version 3.1, CNA
- cisa kev
- Not listed
- not in CISA's catalog
- epss
- 0.6%
- EPSS 0.6% chance of exploitation in 30 days, percentile 51%
- public exploits
- 0
- none known
Summary
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.
Patch / fix
- pypi fast-mcp-telegram 0.19.1
CISA SSVC
- Exploitation
- Proof of concept is public
- Automatable
- yes
- Technical impact
- partial
- Assessed
- 4 mo ago
Exploit prediction
0.65% chance of exploitation in the next 30 days, higher than 51% of all scored CVEs (FIRST EPSS, 2026-11-08).
Exploits and checks
- github.com https://github.com/advisories/GHSA-rxw2-pc8j-vxwm referenced PoC, tagged "exploit" by a source, unverified
CVSS scores
| assigned by | version | score | vector |
|---|---|---|---|
| CNA | 3.1 | 9.4 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:L |
| OSV | 3.1 | 9.4 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:L |
| GitHub | 3.1 | 9.4 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:L |
Affected packages
| ecosystem | package | affected | fixed in |
|---|---|---|---|
| pypi | fast-mcp-telegram | <0.19.1 |
0.19.1 |
Affected products
- leshchenko1979 fast-mcp-telegram
Classification
References
-
github.com
/advisories/GHSA-rxw2-pc8j-vxwm
exploit, advisory
-
web.archive.org
/web/20250926152207/https://github.com/leshchenko1979/fast-mcp-telegram
web
-
github.com
/leshchenko1979/fast-mcp-telegram/security/advisories/GHSA-rxw2-pc8j-vxwm
web
-
nvd.nist.gov
/vuln/detail/CVE-2026-52830
advisory
-
github.com
/alexeyleshchenko/fast-mcp-telegram
package
-
github.com
/pypa/advisory-database/tree/main/vulns/fast-mcp-telegram/PYSEC-2026-2473.yaml
web
-
pypi.org
/project/fast-mcp-telegram
web, package
-
github.com
/leshchenko1979/fast-mcp-telegram
package
Sources
- CVE List CVE-2026-52830
- GitHub Advisory GHSA-rxw2-pc8j-vxwm
- NVD CVE-2026-52830
- OSV PYSEC-2026-2473
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