Werkzeug safe_join() allows Windows special device names

{
  "id": "d6b58544b23eab28531cf091e0876799d5de161d195cbb0d48be9f90f932254c",
  "url": "https://osv.dev/vulnerability/CVE-2026-27199",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "Werkzeug safe_join() allows Windows special device names",
    "summary": "Werkzeug is a comprehensive WSGI web application library. Versions 3.1.5 and below, the safe_join function allows Windows device names as filenames if preceded by other path segments. This was previously reported as GHSA-hgf8-39gv-g3f2, but the added filtering failed to account for the fact that safe_join accepts paths with multiple segments, such as example/NUL. The function send_from_directory uses safe_join to safely serve files at user-specified paths under a directory. If the application is running on Windows, and the requested path ends with a special device name, the file will be opened successfully, but reading will hang indefinitely. This issue has been fixed in version 3.1.6.",
    "evidence": "osv:CVE-2026-27199",
    "products": [],
    "severity": "medium",
    "structured": {
      "id": "CVE-2026-27199",
      "aliases": [
        "CVE-2026-27199",
        "GHSA-29vq-49wr-vm6x",
        "PYSEC-2026-2320"
      ],
      "metrics": [
        {
          "type": "CVSS_V4",
          "score": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/pallets/werkzeug",
              "type": "GIT",
              "events": [
                {
                  "introduced": "0"
                },
                {
                  "fixed": "04da1b5221b7a7b57e82246e4b5741d37a6b2e56"
                },
                {
                  "fixed": "f407712fdc60a09c2b3f4fe7db557703e5d9338d"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "cpe": "cpe:2.3:a:palletsprojects:werkzeug:*:*:*:*:*:*:*:*",
                    "range": [
                      {
                        "introduced": "0"
                      },
                      {
                        "fixed": "3.1.6"
                      }
                    ],
                    "source": "CPE_RANGE"
                  },
                  {
                    "range": [
                      {
                        "fixed": "f407712fdc60a09c2b3f4fe7db557703e5d9338d"
                      }
                    ],
                    "source": "REFERENCES_COMMIT"
                  },
                  {
                    "range": [
                      {
                        "fixed": "04da1b5221b7a7b57e82246e4b5741d37a6b2e56"
                      }
                    ],
                    "source": "REFERENCES_TAG",
                    "original_tag": "3.1.6"
                  }
                ]
              }
            }
          ],
          "versions": [
            "2.2.0",
            "2.2.0a1",
            "2.1.0",
            "2.0.0",
            "2.0.0rc5",
            "2.0.0rc4",
            "2.0.0rc3",
            "2.0.0rc2",
            "2.0.0rc1",
            "1.0.0",
            "1.0.0rc1",
            "0.15.0",
            "0.14",
            "0.13",
            "0.12",
            "0.11",
            "0.10",
            "0.9",
            "0.8",
            "0.7",
            "0.6.2",
            "0.6.1",
            "0.6",
            "0.4.1",
            "0.4",
            "0.3",
            "0.2",
            "0.1"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-27199.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:25.125932149Z",
      "provider": "osv",
      "references": [
        "https://github.com/pallets/werkzeug/releases/tag/3.1.6",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/27xxx/CVE-2026-27199.json",
        "https://github.com/pallets/werkzeug/security/advisories/GHSA-29vq-49wr-vm6x",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-27199",
        "https://github.com/pallets/werkzeug/commit/f407712fdc60a09c2b3f4fe7db557703e5d9338d"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-67"
        ],
        "cna_assigner": "GitHub_M",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/27xxx/CVE-2026-27199.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-27199",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 491818,
  "published_at": "2026-02-21T05:15:53.335+00:00"
}