# CVE-2026-19953

## Summary

- **CVE ID:** CVE-2026-19953
- **Severity:** MEDIUM
- **CVSS Score:** 6.5 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N)
- **CWE:** CWE-1289
- **Published:** Aug 31, 2026
- **Last Modified:** Sep 1, 2026

## Description

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.

## Affected Products

- Unknown product (0)

## References

- [CNA](https://github.com/libwww-perl/URI/commit/956619a9e94f86d8d2c529b4e06a3674c54a73e7.patch)
- [CNA](https://github.com/libwww-perl/URI/pull/191)
- [CNA](https://metacpan.org/release/OALDERS/URI-5.36/changes)
- [CNA](https://www.rfc-editor.org/rfc/rfc5891#section-5.2)
- [CVE](http://www.openwall.com/lists/oss-security/2026/08/31/14)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.37%
- **EPSS Percentile:** 30.6

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-10._