---
cve: "CVE-2026-19953"
severity: "MEDIUM"
cvss: 6.5
epss: "3.4%"
vendor: "Generic Security"
kev: false
exploited: false
published: "2026-08-31 18:17:14"
tags: [cve, security, medium]
source: tsecurity.de CVE-Dossier
exported: "2026-09-07T03:46:21+02:00"
---

# CVE-2026-19953

> 6.5 MEDIUM

## Beschreibung

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.

## CVSS-Vektor

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

| Metrik | Wert | Bewertung |
|---|---|---|
| AV Angriffsvektor | Netzwerk | bad |
| AC Komplexität | Gering | bad |
| PR Privilegien | Keine | bad |
| UI Interaktion | Keine | bad |
| S Scope | Unverändert | good |
| C Vertraulichkeit | Gering | warn |
| I Integrität | Gering | warn |
| A Verfügbarkeit | Keine | good |

## Patch verfügbar (OSV)

- b265e58bb1ead8133eb7614b76bb7891bd96cea0 (Commit)
- 956619a9e94f86d8d2c529b4e06a3674c54a73e7 (Commit)

## Referenzen

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

---
_Exportiert aus dem [tsecurity.de CVE-Dossier](https://tsecurity.de/cve?cve=CVE-2026-19953) · Datenquellen: EUVD (ENISA), NVD, OSV, CISA KEV, FIRST EPSS, Exploit-DB, BSI BITS_