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EUVD-2026-358917

fkie_cve-2026-55557

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.

GHSA-m9mq-7m7q-xc6p — browse-mcp has an arbitrary file write via unconfined download and state paths

Affected: npm: browse-mcp

### 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 th…