CVE-2026-19953: URI versions before 5.36 for Perl encode non-NFC host names to non-standard punycode labels via missing normalization in nameprep
Vendor not named in the CVE record · URI
Fixed in 5.36 · Affected: URI before 5.36 · Exploitation: unlikely (under 1%)
Not in CyberSIXT coverage yet: no article names this CVE. This page shows the public record.
Higher than 13% of scored CVEs
DescriptionCVE.org
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 products1
From the CVE record. A product or version that is not listed is unknown, not unaffected.
- URIbefore 5.36
On the Atlas
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- Exploitation
- Unlikely (under 1%). EPSS under 1%, or no score yet.
- CISA KEV
- Not listed
- Public check
- No public nuclei template
- Published
- August 2026
CoverageNo articles yet
No CyberSIXT article names CVE-2026-19953 yet, so there is no coverage timeline, action brief or change log for it. Everything on this page comes from the public CVE record, CISA KEV, EPSS and the nuclei template index. Search the archive or see the CVEs in the news.