CVE-2026-52830
fast-mcp-telegram: Bearer token path traversal bypasses reserved Telegram session protection
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.
INFO
Published Date :
July 2, 2026, 9:16 p.m.
Last Modified :
Oct. 25, 2026, 9:10 p.m.
Remotely Exploit :
Yes !
Source :
[email protected]
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS | 134c704f-9b21-4f2e-91b3-4a467353bcc0 | |||||
| CVSS 3.1 | CRITICAL | [email protected] |
Solution
- Update fast-mcp-telegram to version 0.19.1.
- Remove or restrict access to session files.
- Validate all user inputs carefully.
Public PoC/Exploit Available at Github
CVE-2026-52830 has a 2 public
PoC/Exploit available at Github.
Go to the Public Exploits tab to see the list.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-52830.
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-52830 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-52830
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
A curated timeline of real AI agent security incidents, breaches, and vulnerabilities (2024-2026). Every entry sourced and dated.
ai-agent-security ai-agents ai-security awesome-list cybersecurity llm-security mcp-security prompt-injection supply-chain-security adversarial-attacks agent-security agentic-ai ai-attacks ai-safety cve incident-response owasp red-team security-research vulnerability
Static scanner for MCP-connected AI agent pipelines — 225 rules across 11 categories, 12 compliance frameworks, OWASP Agentic 10/10 + MCP 10/10, GitHub Action, SARIF, public CVE-to-rule ledger.
ai-agent ai-security claude-code github-action mcp mcp-security owasp sarif scanner security supply-chain-security tool-poisoning ai-agent-security ai-safety security-scanner static-analysis
Python Dockerfile Shell TypeScript HTML Makefile
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-52830 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-52830 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
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CVE Translated by [email protected]
Oct. 25, 2026
Action Type Old Value New Value Added Translation Title: fast-mcp-telegram de leshchenko1979, Description: fast-mcp-telegram es un servidor MCP de Telegram. Antes de la versión 0.19.1, fast-mcp-telegram valida los tokens Bearer HTTP uniendo la cadena de token en bruto en una ruta de archivo de sesión. El verificador rechaza el token reservado exacto ’telegram’, pero no rechaza los separadores de ruta ni normaliza la ruta antes de verificar si el archivo de sesión existe. Un cliente HTTP remoto puede, por lo tanto, autenticarse como la sesión heredada predeterminada con un token como .. / fast-mcp-telegram/telegram cuando el archivo de sesión predeterminado documentado ~/.config/fast-mcp-telegram/telegram.session existe. Esto elude el control de nombre de sesión reservado que está destinado a evitar que las sesiones multiusuario HTTP colisionen con la cuenta stdio predeterminada o heredada. Con las herramientas MCP con prefijo de cuenta habilitadas, el atacante todavía ve y llama a las herramientas con prefijo para la cuenta predeterminada, por lo que el middleware de prefijo no detiene la elusión de la selección de sesión. Esta vulnerabilidad se corrige en la versión 0.19.1. -
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Jul. 06, 2026
Action Type Old Value New Value Added Reference https://github.com/advisories/GHSA-rxw2-pc8j-vxwm Added SSVC {'id': 'CVE-2026-52830', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'poc'}, {'automatable': 'yes'}, {'technicalImpact': 'partial'}], 'version': '2.0.3', 'timestamp': '2026-07-06T14:35:51.099192Z'} -
New CVE Received by [email protected]
Jul. 02, 2026
Action Type Old Value New Value Added Affected [{'vendor': 'leshchenko1979', 'product': 'fast-mcp-telegram', 'versions': [{'status': 'affected', 'version': '< 0.19.1'}]}] Added 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. Added CVSS V3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:L Added CWE CWE-287 Added CWE CWE-22 Added Reference https://github.com/advisories/GHSA-rxw2-pc8j-vxwm Added Reference https://web.archive.org/web/20250926152207/https://github.com/leshchenko1979/fast-mcp-telegram