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Vulnerability · Published Aug 25, 2026 · Assigned by GitHub_M

CVE-2026-55557browse-mcp: Arbitrary file write via unconfined download and state paths

High 8.6

In plain English

A high-severity path traversal in browse-mcp from That1Drifter. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 15% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 4.0)8.6High
Exploit odds (30 days)0.2%top 85.0% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known

Official description

browse-mcp is a Playwright-based headless-browser MCP server for MCP-capable agents. Prior to 0.8.2, browser_download writes a fetched response body to join(save_dir, filename) without validating the caller-controlled save_dir, while browser_save_state and browser_load_state honor a caller-controlled path unchanged. A malicious MCP client, or an autonomous agent steered by indirect prompt injection on a visited page, can choose an arbitrary save_dir or state path and a URL whose response body becomes attacker-controlled file contents, allowing writes to any path the process can reach, including ~/.bashrc, autostart entries, or cron files, and potentially leading to host code execution. The force_fetch fallback also uses a raw fetch() that bypasses the BROWSE_MCP_ALLOWED_ORIGINS origin fence. This issue is fixed in version 0.8.2.

Affected packages & fixed versions

EcosystemPackageFixed inAdvisory
npmbrowse-mcp0.8.2GHSA-m9mq-7m7q-xc6p

Affected products (as reported)

VendorProductVersions
That1Drifter browse-mcp < 0.8.2

Weakness: CWE-22 · Vector: CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

References