CVE-2026-19953
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. 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.
Published · last modified .
CVSS v3 metric
CVSS v3 base score 6.5 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N.
EPSS exploit prediction
EPSS: 0.002 (12.7th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 13th percentile — 12.7% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.004 · newest: 0.002 · change: -0.001
Weakness classification (CWE)
References
- 9b29abf9-4ab0-4765-b253-1875cd9b441e (patch)
- 9b29abf9-4ab0-4765-b253-1875cd9b441e (issue-tracking)
- 9b29abf9-4ab0-4765-b253-1875cd9b441e (release-notes)
- 9b29abf9-4ab0-4765-b253-1875cd9b441e (technical-description)
- af854a3a-2127-422b-91ae-364da2661108
Frequently asked questions
- What is CVE-2026-19953?
- CVE-2026-19953 is a medium-severity vulnerability, classified under CWE-1289. CVSS score: 6.5/10. Published 2026-08-31.
- How severe is CVE-2026-19953?
- Medium severity. CVSS v3 base score is 6.5 out of 10.