PYSEC-2026-4312
Vulnerability from pysec - Published: 2026-10-15 10:22 - Updated: 2026-10-15 14:38Werkzeug's safe_join function allows Windows device names as filenames when they have an empty ADS marker on NTFS.
This was previously reported as https://github.com/pallets/werkzeug/security/advisories/GHSA-hgf8-39gv-g3f2, but the added filtering failed to account for the fact Windows allows special device names with an empty ADS marker, such as NUL:.
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 NTFS, and the requested path ends with a special device name, the file will be opened successfully, but reading will hang indefinitely.
| Name | purl | werkzeug | pkg:pypi/werkzeug |
|---|
{
"affected": [
{
"package": {
"ecosystem": "PyPI",
"name": "werkzeug",
"purl": "pkg:pypi/werkzeug"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "3.1.9"
}
],
"type": "ECOSYSTEM"
}
],
"versions": [
"0.1",
"0.10",
"0.10.1",
"0.10.2",
"0.10.3",
"0.10.4",
"0.11",
"0.11.1",
"0.11.10",
"0.11.11",
"0.11.12",
"0.11.13",
"0.11.14",
"0.11.15",
"0.11.2",
"0.11.3",
"0.11.4",
"0.11.5",
"0.11.6",
"0.11.7",
"0.11.8",
"0.11.9",
"0.12",
"0.12.1",
"0.12.2",
"0.13",
"0.14",
"0.14.1",
"0.15.0",
"0.15.1",
"0.15.2",
"0.15.3",
"0.15.4",
"0.15.5",
"0.15.6",
"0.16.0",
"0.16.1",
"0.2",
"0.3",
"0.3.1",
"0.4",
"0.4.1",
"0.5",
"0.5.1",
"0.6",
"0.6.1",
"0.6.2",
"0.7",
"0.7.1",
"0.7.2",
"0.8",
"0.8.1",
"0.8.2",
"0.8.3",
"0.9",
"0.9.1",
"0.9.2",
"0.9.3",
"0.9.4",
"0.9.5",
"0.9.6",
"1.0.0",
"1.0.0rc1",
"1.0.1",
"2.0.0",
"2.0.0rc1",
"2.0.0rc2",
"2.0.0rc3",
"2.0.0rc4",
"2.0.0rc5",
"2.0.1",
"2.0.2",
"2.0.3",
"2.1.0",
"2.1.1",
"2.1.2",
"2.2.0",
"2.2.0a1",
"2.2.1",
"2.2.2",
"2.2.3",
"2.3.0",
"2.3.1",
"2.3.2",
"2.3.3",
"2.3.4",
"2.3.5",
"2.3.6",
"2.3.7",
"2.3.8",
"3.0.0",
"3.0.1",
"3.0.2",
"3.0.3",
"3.0.4",
"3.0.5",
"3.0.6",
"3.1.0",
"3.1.1",
"3.1.2",
"3.1.3",
"3.1.4",
"3.1.5",
"3.1.6",
"3.1.7",
"3.1.8"
]
}
],
"aliases": [
"CVE-2026-102598",
"GHSA-g6x2-hccm-hh4m"
],
"details": "Werkzeug\u0027s `safe_join` function allows Windows device names as filenames when they have an empty ADS marker on NTFS.\n\nThis was previously reported as https://github.com/pallets/werkzeug/security/advisories/GHSA-hgf8-39gv-g3f2, but the added filtering failed to account for the fact Windows allows special device names with an empty ADS marker, such as `NUL:`.\n\n`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 NTFS, and the requested path ends with a special device name, the file will be opened successfully, but reading will hang indefinitely.",
"id": "PYSEC-2026-4312",
"modified": "2026-10-15T14:38:14.997317Z",
"published": "2026-10-15T10:22:46.332690Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/pallets/werkzeug/security/advisories/GHSA-g6x2-hccm-hh4m"
},
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-102598"
},
{
"type": "WEB",
"url": "https://github.com/pallets/werkzeug/pull/3309"
},
{
"type": "WEB",
"url": "https://github.com/pallets/werkzeug/commit/8d77320bcdf3a34941ec06dcf16b03c065cd21b6"
},
{
"type": "PACKAGE",
"url": "https://github.com/pallets/werkzeug"
},
{
"type": "WEB",
"url": "https://github.com/pallets/werkzeug/releases/tag/3.1.9"
},
{
"type": "PACKAGE",
"url": "https://pypi.org/project/werkzeug"
},
{
"type": "ADVISORY",
"url": "https://github.com/advisories/GHSA-g6x2-hccm-hh4m"
}
],
"severity": [
{
"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",
"type": "CVSS_V4"
}
],
"summary": "Werkzeug safe_join() allows Windows special device names"
}
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