SSRF (Server-Side Request Forgery) in auth-fetch-mcp (CVE-2026-49857)
Summary
SSRF in auth-fetch-mcp (CVE-2026-49857). Confidential information can be exposed externally. Exploitable via false. Mitigation: upgrade to 3.0.2 or later.
Original description
The description as published by the source.
auth-fetch-mcp is an MCP server that lets AI assistants fetch content from authenticated web pages. Version 3.0.1 implements SSRF protection in assertSafeUrl() (src/security.ts) to block requests to private and loopback addresses. However, the isPrivateV6() function fails to detect IPv4-mapped IPv6 loopback addresses in their hex-normalized form. When an attacker supplies a URL such as http://[::ffff:127.0.0.1]:PORT/, the Node.js WHATWG URL parser silently normalizes the host to [::ffff:7f00:1]. Because net.isIPv4('7f00:1') returns false, the private-IP check is bypassed and the URL is passed to the browser or HTTP client, allowing the MCP tool to reach loopback services that are supposed to be blocked. The issue is exploitable under default configuration without any special environment variable. Version 3.0.1 patches the issue.
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-2026-49857 has been found in auth-fetch-mcp.
Attackers can target a specific entry point like false over the network to misuse the product.
Confidential information can be exposed externally. CVSS score: 7.4/10.
What to do: upgrade auth-fetch-mcp to 3.0.2 or later.
If unsure, ask your IT team or search "auth-fetch-mcp CVE-2026-49857" on the vendor's site.
CVE-2026-49857 (auth-fetch-mcp) — CWE-918 / CVSS v3 7.4
Attack vector: remote (network-reachable) / unauthenticated
Attack surface: false / auth_fetch / download_media / INTERNAL_SECRET_MARKER
Patched: 3.0.2 — 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.
SSRF (CWE-918) exists in auth-fetch-mcp. Attackers reach the vulnerable code path via false without authentication.
Check the vendor advisory for the affected versions of auth-fetch-mcp. Attack surface: false / auth_fetch / download_media / INTERNAL_SECRET_MARKER.
Severity: High (CVSS 7.4/10). Confidential information can be exposed externally.
Update to 3.0.2.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'auth-fetch-mcp' . 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
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1Identify exposure identify
grep -r 'auth-fetch-mcp' . | 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
auth-fetch-mcpを grep し、稼働しているサービス・バージョンを把握する。 -
2Apply patch patch
Upgrade auth-fetch-mcp to 3.0.2ステージング環境で 3.0.2 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。
-
3Post-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
References
- advisory github.com
- advisory github.com
- advisory nvd.nist.gov
- package github.com
- patch github.com
- web github.com
- web github.com