{"id":"DEBIAN-CVE-2026-19953","details":"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.","modified":"2026-09-04T08:47:34.537303646Z","published":"2026-08-31T18:17:14.320Z","upstream":["CVE-2026-19953"],"references":[{"type":"ADVISORY","url":"https://security-tracker.debian.org/tracker/CVE-2026-19953"}],"affected":[{"package":{"name":"liburi-perl","ecosystem":"Debian:12","purl":"pkg:deb/debian/liburi-perl?arch=source&distro=bookworm"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["5.17-1","5.19-1","5.19-2","5.21-1","5.25-1","5.26-1","5.27-1","5.28-1","5.29-1","5.30-1","5.34-1","5.34-2","5.35-1","5.36-1"],"ecosystem_specific":{"urgency":"not yet assigned"},"database_specific":{"source":"https://storage.googleapis.com/osv-test-debian-osv/debian-cve-osv/DEBIAN-CVE-2026-19953.json"}},{"package":{"name":"liburi-perl","ecosystem":"Debian:13","purl":"pkg:deb/debian/liburi-perl?arch=source&distro=trixie"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["5.30-1","5.34-1","5.34-2","5.35-1","5.36-1"],"ecosystem_specific":{"urgency":"not yet assigned"},"database_specific":{"source":"https://storage.googleapis.com/osv-test-debian-osv/debian-cve-osv/DEBIAN-CVE-2026-19953.json"}},{"package":{"name":"liburi-perl","ecosystem":"Debian:14","purl":"pkg:deb/debian/liburi-perl?arch=source&distro=forky"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"5.36-1"}]}],"versions":["5.30-1","5.34-1","5.34-2","5.35-1"],"ecosystem_specific":{"urgency":"not yet assigned"},"database_specific":{"source":"https://storage.googleapis.com/osv-test-debian-osv/debian-cve-osv/DEBIAN-CVE-2026-19953.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N"}]}