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

{
  "id": "236fd087443837ed7c25e74cb9b08344e6d448282741f8b3d07fee4aa65c74f8",
  "url": "https://osv.dev/vulnerability/CVE-2026-55557",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "browse-mcp: Arbitrary file write via unconfined download and state paths",
    "summary": "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.",
    "evidence": "osv:CVE-2026-55557",
    "products": [],
    "severity": "high",
    "structured": {
      "id": "CVE-2026-55557",
      "aliases": [
        "CVE-2026-55557",
        "GHSA-m9mq-7m7q-xc6p"
      ],
      "metrics": [
        {
          "type": "CVSS_V4",
          "score": "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"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/that1drifter/browse-mcp",
              "type": "GIT",
              "events": [
                {
                  "introduced": "0"
                },
                {
                  "fixed": "46d75f467d1a8f3c88b7224eacfd4038a969e7e8"
                },
                {
                  "fixed": "5352a4a56f626254b445bfa07e4bb48c5aad15c1"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "range": [
                      {
                        "introduced": "0"
                      },
                      {
                        "fixed": "0.8.2"
                      }
                    ],
                    "source": "AFFECTED_FIELD",
                    "strategy": "StringRangeExpression"
                  },
                  {
                    "range": [
                      {
                        "fixed": "5352a4a56f626254b445bfa07e4bb48c5aad15c1"
                      }
                    ],
                    "source": "REFERENCES_COMMIT"
                  },
                  {
                    "range": [
                      {
                        "fixed": "46d75f467d1a8f3c88b7224eacfd4038a969e7e8"
                      }
                    ],
                    "source": "REFERENCES_TAG",
                    "original_tag": "v0.8.2"
                  }
                ]
              }
            }
          ],
          "versions": [
            "v0.8.1",
            "v0.8.0",
            "v0.7.0",
            "v0.6.0",
            "v0.5.0",
            "v0.4.1",
            "v0.4.0",
            "v0.3.0",
            "v0.2.1"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-55557.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:28.784896503Z",
      "provider": "osv",
      "references": [
        "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",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/55xxx/CVE-2026-55557.json",
        "https://github.com/That1Drifter/browse-mcp/security/advisories/GHSA-m9mq-7m7q-xc6p",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-55557",
        "https://github.com/That1Drifter/browse-mcp/commit/5352a4a56f626254b445bfa07e4bb48c5aad15c1",
        "https://github.com/That1Drifter/browse-mcp/pull/58"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-22"
        ],
        "cna_assigner": "GitHub_M",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/55xxx/CVE-2026-55557.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-55557",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 495754,
  "published_at": "2026-08-25T16:28:07.368+00:00"
}