BREW-CPM-CVE-2026-19953 (CVE-2026-19953)

Vulnerability from osv_homebrew – Published: 2026-09-09 23:48 – Updated: 2026-09-09 23:48 – Source website
VLAI
Summary
URI versions before 5.36 for Perl encode non-NFC host names to non-standard punycode labels via missing normalization in nameprep
Details

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.

Severity
6.5 (Medium)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
References
To clipboard 

{
  "affected": [
    {
      "ecosystem_specific": {
        "fix": null,
        "range_state": "affected",
        "resource": "URI",
        "resource_purl": "pkg:cpan/OALDERS/URI@5.35",
        "upstream_fixed_in": "5.36"
      },
      "package": {
        "ecosystem": "Homebrew",
        "name": "cpm",
        "purl": "pkg:brew/cpm"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "database_specific": {
    "confidence": "medium",
    "source": "matched",
    "strategy": "cpansa",
    "upstream_evidence": [
      {
        "ecosystem": "CPAN",
        "key": "pkg:cpan/OALDERS/URI@5.35",
        "name": "URI",
        "resource": "URI",
        "strategy": "cpansa",
        "subject_version": "5.35"
      }
    ]
  },
  "details": "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": "BREW-cpm-CVE-2026-19953",
  "modified": "2026-09-09T23:48:52Z",
  "published": "2026-09-09T23:48:52Z",
  "references": [
    {
      "type": "WEB",
      "url": "http://www.openwall.com/lists/oss-security/2026/08/31/14"
    },
    {
      "type": "WEB",
      "url": "https://cpan.org/modules"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/19xxx/CVE-2026-19953.json"
    },
    {
      "type": "ADVISORY",
      "url": "https://metacpan.org/release/OALDERS/URI-5.36/changes"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-19953"
    },
    {
      "type": "REPORT",
      "url": "https://github.com/libwww-perl/URI/pull/191"
    },
    {
      "type": "FIX",
      "url": "https://github.com/libwww-perl/URI/commit/956619a9e94f86d8d2c529b4e06a3674c54a73e7.patch"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/libwww-perl/URI"
    },
    {
      "type": "ARTICLE",
      "url": "https://www.rfc-editor.org/rfc/rfc5891#section-5.2"
    }
  ],
  "schema_version": "1.7.3",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "URI versions before 5.36 for Perl encode non-NFC host names to non-standard punycode labels via missing normalization in nameprep",
  "upstream": [
    "CVE-2026-19953"
  ]
}



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