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CVE-2026-55557

Path Traversal in browse-mcp (CVE-2026-55557)

Summary

Path traversal in browse-mcp (CVE-2026-55557). Risk of unauthorized operations or information disclosure. Exploitable via browser_download. Mitigation: upgrade to 0.8.2 or later.

Original description

The description as published by the source.

Impact

browser_download wrote a fetched file to join(save_dir, filename) with no validation of save_dir, and browser_save_state / browser_load_state honored an explicit path unchanged. The MCP caller controls these arguments (a malicious MCP client, or an autonomous agent steered by indirect prompt injection on a visited page), so an attacker could supply an arbitrary save_dir (or state path) together with a URL whose response body became the file contents, writing attacker-controlled bytes to any path the process can reach (for example ~/.bashrc, an autostart entry, or a cron file). That is an arbitrary file write that can lead to host code execution. The force_fetch fallback additionally used a raw fetch() that bypassed the BROWSE_MCP_ALLOWED_ORIGINS origin fence.

Estimated severity: CVSS 3.1 around 7.8 (High) for the local / agent-mediated case.

Patches

Fixed in 0.8.2. save_dir is confined under the download root (~/.browse-mcp/downloads) and the explicit state path under ~/.browse-mcp/state; absolute paths and .. escapes are rejected, and download filenames are reduced to a bare basename. force_fetch now also honors the origin fence. Data roots remain relocatable via BROWSE_MCP_HOME. Upgrade to browse-mcp 0.8.2.

Workarounds

Restrict the exposed tools with BROWSE_MCP_TOOLS to a set that excludes browser_download, browser_save_state, and browser_load_state (for example the hardened recipe in SECURITY.md). Note tha…

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-2026-55557 has been found in browse-mcp.
Attackers can target a specific entry point like browser_download over the network to misuse the product.
Risk of unauthorized operations or information disclosure.
What to do: upgrade browse-mcp to 0.8.2 or later.
If unsure, ask your IT team or search "browse-mcp CVE-2026-55557" on the vendor's site.

CVE-2026-55557 (browse-mcp) — CWE-22
Attack surface: browser_download / save_dir / browser_save_state / browser_load_state
Patched: 0.8.2 — 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.

❓ What is the problem

Path traversal (CWE-22) exists in browse-mcp. Attackers reach the vulnerable code path via browser_download.

📍 Affected scope

Check the vendor advisory for the affected versions of browse-mcp. Attack surface: browser_download / save_dir / browser_save_state / browser_load_state.

🔥 Severity

Severity: ?. Risk of unauthorized operations or information disclosure.

🔧 How to fix

Update to 0.8.2.

🛡️ 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 'browse-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

  1. 1
    Identify exposure identify 
    grep -r 'browse-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 browse-mcp 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 browse-mcp to 0.8.2

    ステージング環境で 0.8.2 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。

  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

npm browse-mcp
[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"0.8.2"}]}]

References

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