CVE-2026-19953 (GCVE-0-2026-19953)

Vulnerability from cvelistv5 – Published: 2026-08-31 17:29 – Updated: 2026-09-01 15:16
VLAI
Title
URI versions before 5.36 for Perl encode non-NFC host names to non-standard punycode labels via missing normalization in nameprep
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.
Severity
6.5 (Medium)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
SSVC
Exploitation: none Automatable: yes Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-09-01 15:16 UTC
CWE
  • CWE-1289 - Improper Validation of Unsafe Equivalence in Input
Assigner
CPANSec CNA under the redhat root
CNA scorecard C 62/100 over 369 records in the last 180 days details
References
Impacted products
Vendor Product Version CPE status
Affected: 0 , < 5.36 (custom)
Credits
Naseeb Dangi (naseeb0), Nankai University
Show details on NVD website
To clipboard 

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