URI versions before 5.36 for Perl encode non-NFC host names to non-standard punycode labels via missing normalization in nameprep

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-19953
StatePUBLISHED
AssignerCPANSec
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-08-31 18:17:14 UTC
Updated2026-09-03 16:41:09 UTC
DescriptionURI 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.

Risk And Classification

Primary CVSS: v3.1 6.5 MEDIUM from ADP

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N

EPSS: 0.003730000 probability, percentile 0.304320000 (date 2026-09-07)

Problem Types: CWE-1289 | CWE-1289 CWE-1289 Improper Validation of Unsafe Equivalence in Input

VersionSourceTypeScoreSeverityVector
3.1ADPDECLARED6.5MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
3.1134c704f-9b21-4f2e-91b3-4a467353bcc0Secondary6.5MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
Low
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N

References

ReferenceSourceLinkTags
www.openwall.com/lists/oss-security/2026/08/31/14 af854a3a-2127-422b-91ae-364da2661108 www.openwall.com
metacpan.org/release/OALDERS/URI-5.36/changes 9b29abf9-4ab0-4765-b253-1875cd9b441e metacpan.org
github.com/libwww-perl/URI/commit/956619a9e94f86d8d2c529b4e06a3674c54a73... 9b29abf9-4ab0-4765-b253-1875cd9b441e github.com
www.rfc-editor.org/rfc/rfc5891 9b29abf9-4ab0-4765-b253-1875cd9b441e www.rfc-editor.org
github.com/libwww-perl/URI/pull/191 9b29abf9-4ab0-4765-b253-1875cd9b441e github.com
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

Vendor Comments And Credit

Discovery Credit

CNA: Naseeb Dangi (naseeb0), Nankai University (en)

Additional Advisory Data

Solutions

CNA: Upgrade to URI 5.36 or later.

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