What’s Vulnerable › Vulnerabilities

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

• Severity: high (CVSS 8.6 v4.0)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-08-25 · updated 2026-09-09
• Weakness: CWE-22

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 products

• That1Drifter browse-mcp: before 0.8.2

References

• https://github.com/That1Drifter/browse-mcp/blob/v0.8.2/CHANGELOG.md#082---2026-06-13
• https://github.com/That1Drifter/browse-mcp/commit/5352a4a56f626254b445bfa07e4bb48c5aad15c1
• https://github.com/That1Drifter/browse-mcp/pull/58
• https://github.com/That1Drifter/browse-mcp/releases/tag/v0.8.2
• https://github.com/That1Drifter/browse-mcp/security/advisories/GHSA-m9mq-7m7q-xc6p

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