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CVE-2026-19953 on Cyberus Linux 26.05

Aliases: CVE-2026-19953

Packages: perlPackages.URI

Status: Plausible

Advisory Information

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.

Updates

2026-08-31 17:42 CEST

Metadata changes:

  • Status for package perlPackages.URI: “Plausible”

2026-08-31 17:41 CEST

Metadata changes:

  • Status for package perlPackages.URI: “New”

(Amended on: 2026-08-31 17:42 CEST)