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

> A malicious MCP client or prompt-injected agent can write arbitrary files to sensitive system paths, potentially leading to host code execution.

- **Severity:** High 8.6 (`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`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 25 Aug 2026
- **Updated:** 25 Aug 2026
- **Also known as:** GHSA-m9mq-7m7q-xc6p

## What is CVE-2026-55557?

CVE-2026-55557 is a high-severity path traversal vulnerability in That1Drifter browse-mcp, published on 25 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### 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.

Weakness: CWE-22 (Improper Limitation of a Pathname to a Restricted Directory)

## Which versions are affected by CVE-2026-55557?

2 open source packages ship an affected version, including browse-mcp.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `browse-mcp` | npm | All versions | 0.8.2 |
| `browse-mcp` | npm | All versions | 0.8.2 |

## How do I fix CVE-2026-55557?

Upgrade browse-mcp to 0.8.2 or later.

## Is CVE-2026-55557 being exploited?

There is no known exploitation of CVE-2026-55557 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-55557 and fix it if it is affected.

What it is: CVE-2026-55557 is a high-severity path traversal vulnerability in That1Drifter browse-mcp, published on 25 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-55557 in the wild and no public exploit code.

Affected packages and fixed versions:
- browse-mcp (npm): affected all versions; fixed in 0.8.2
- browse-mcp (npm): affected all versions; fixed in 0.8.2

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-55557/ (Markdown: https://insights.sbomify.com/CVE-2026-55557/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-55557
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-55557
- OSV: https://osv.dev/vulnerability/CVE-2026-55557

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-55557/
Summaries are generated and may contain mistakes; the official description above is the record.