FKIE_CVE-2026-19953

Vulnerability from fkie_nvd - Published: 2026-08-31 18:17 - Updated: 2026-08-31 21:17
Severity
Summary
URI versions before 5.36 for Perl encode non-NFC host names to non-standard punycode labels via missing normalization in nameprep. nameprep lowercases each host label but performs no Unicode normalization. IDNA requires a label to be normalized to Form C before it is encoded (RFC 5891), so a label that is not already in NFC is encoded to a different A-label than its normalized form. A label built from the precomposed Devanagari sequence U+0958 U+093E encodes to xn--72b5c without normalization but to xn--11b2fg after NFC normalization, and xn--72b5c does not round-trip back to the original label. Any caller that reads host() from a URI built from untrusted input and uses it for a security decision (an allow or deny list, an SSRF filter, deduplication, a cache key) sees the non-standard label, while a client that fetches the same URL resolves the NFC form, so the check and the fetch can disagree about the host.
References
9b29abf9-4ab0-4765-b253-1875cd9b441ehttps://github.com/libwww-perl/URI/commit/956619a9e94f86d8d2c529b4e06a3674c54a73e7.patch
9b29abf9-4ab0-4765-b253-1875cd9b441ehttps://github.com/libwww-perl/URI/pull/191
9b29abf9-4ab0-4765-b253-1875cd9b441ehttps://metacpan.org/release/OALDERS/URI-5.36/changes
9b29abf9-4ab0-4765-b253-1875cd9b441ehttps://www.rfc-editor.org/rfc/rfc5891#section-5.2
af854a3a-2127-422b-91ae-364da2661108http://www.openwall.com/lists/oss-security/2026/08/31/14
Impacted products
Vendor Product Version
To clipboard 

{
  "affected": [
    {
      "affectedData": [
        {
          "collectionURL": "https://cpan.org/modules",
          "defaultStatus": "unaffected",
          "modules": [
            "URI"
          ],
          "packageName": "URI",
          "packageURL": "pkg:cpan/URI",
          "programFiles": [
            "lib/URI/_idna.pm"
          ],
          "programRoutines": [
            {
              "name": "URI::_idna::nameprep"
            }
          ],
          "repo": "https://github.com/libwww-perl/URI",
          "versions": [
            {
              "lessThan": "5.36",
              "status": "affected",
              "version": "0",
              "versionType": "custom"
            }
          ]
        }
      ],
      "source": "9b29abf9-4ab0-4765-b253-1875cd9b441e"
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "URI versions before 5.36 for Perl encode non-NFC host names to non-standard punycode labels via missing normalization in nameprep.\n\nnameprep lowercases each host label but performs no Unicode normalization. IDNA requires a label to be normalized to Form C before it is encoded (RFC 5891), so a label that is not already in NFC is encoded to a different A-label than its normalized form. A label built from the precomposed Devanagari sequence U+0958 U+093E encodes to xn--72b5c without normalization but to xn--11b2fg after NFC normalization, and xn--72b5c does not round-trip back to the original label.\n\nAny caller that reads host() from a URI built from untrusted input and uses it for a security decision (an allow or deny list, an SSRF filter, deduplication, a cache key) sees the non-standard label, while a client that fetches the same URL resolves the NFC form, so the check and the fetch can disagree about the host."
    }
  ],
  "id": "CVE-2026-19953",
  "lastModified": "2026-08-31T21:17:07.253",
  "metrics": {},
  "published": "2026-08-31T18:17:14.320",
  "references": [
    {
      "source": "9b29abf9-4ab0-4765-b253-1875cd9b441e",
      "url": "https://github.com/libwww-perl/URI/commit/956619a9e94f86d8d2c529b4e06a3674c54a73e7.patch"
    },
    {
      "source": "9b29abf9-4ab0-4765-b253-1875cd9b441e",
      "url": "https://github.com/libwww-perl/URI/pull/191"
    },
    {
      "source": "9b29abf9-4ab0-4765-b253-1875cd9b441e",
      "url": "https://metacpan.org/release/OALDERS/URI-5.36/changes"
    },
    {
      "source": "9b29abf9-4ab0-4765-b253-1875cd9b441e",
      "url": "https://www.rfc-editor.org/rfc/rfc5891#section-5.2"
    },
    {
      "source": "af854a3a-2127-422b-91ae-364da2661108",
      "url": "http://www.openwall.com/lists/oss-security/2026/08/31/14"
    }
  ],
  "sourceIdentifier": "9b29abf9-4ab0-4765-b253-1875cd9b441e",
  "vulnStatus": "Received",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-1289"
        }
      ],
      "source": "9b29abf9-4ab0-4765-b253-1875cd9b441e",
      "type": "Secondary"
    }
  ]
}



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