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CVE-2026-52830 critical CVSS 9.4

Path Traversal in fast-mcp-telegram (CVE-2026-52830)

Summary

Path traversal in fast-mcp-telegram (CVE-2026-52830). Confidential information can be exposed externally. Exploitable via telegram. Mitigation: upgrade to 0.19.1 or later.

Original description

The description as published by the source.

Summary

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.

Impact

An unauthenticated network client can access the Telegram account represented by the default telegram.session file without knowing a generated bearer token, if that legacy or default session file is present on a server running HTTP auth. The attacker can then call Telegram MCP tools as that account, including message reading, message sending, MTProto API calls, and attachment-producing tool surfaces available to the session.

Technical details

SessionFileTokenVerifier.verify_token() strips whitespace and rejects exact reserved names:

if token.lower() in RESERVED_SESSION_NAMES:
    return None

It th…

Source: GitHub Security Advisories (Global) NVD GitHub Advisory

Auto-generated summary

Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.

A vulnerability tracked as CVE-2026-52830 has been found in fast-mcp-telegram.
Attackers can target a specific entry point like telegram over the network to misuse the product.
Confidential information can be exposed externally. CVSS score: 9.4/10.
What to do: upgrade fast-mcp-telegram to 0.19.1 or later.
If unsure, ask your IT team or search "fast-mcp-telegram CVE-2026-52830" on the vendor's site.

CVE-2026-52830 (fast-mcp-telegram) — CWE-22 / CVSS v3 9.4
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: telegram / telegram.session / session_name / master
Patched: 0.19.1 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.

❓ What is the problem

Path traversal (CWE-22) exists in fast-mcp-telegram. Attackers reach the vulnerable code path via telegram without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of fast-mcp-telegram. Attack surface: telegram / telegram.session / session_name / master.

🔥 Severity

Severity: Critical (CVSS 9.4/10). Confidential information can be exposed externally.

🔧 How to fix

Update to 0.19.1.

🛡️ Workaround

Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.

🔍 Detection

Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'fast-mcp-telegram' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.

Response actions

Concrete steps and command examples for SOC/SRE teams to execute in order

  1. 1
    Identify exposure identify 
    grep -r 'fast-mcp-telegram' . | grep -v node_modules

    リポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で fast-mcp-telegram を grep し、稼働しているサービス・バージョンを把握する。

  2. 2
    Apply patch patch 
    Upgrade fast-mcp-telegram to 0.19.1

    ステージング環境で 0.19.1 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。

  3. 3
    Post-deployment verification verify 
    Confirm patched version is live in production

    パッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。

Affected packages

pip fast-mcp-telegram
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"0.19.1"}]}]
PyPI fast-mcp-telegram
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"0.19.1"}]}]

References

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