DocumentationOverview
About vulnerability
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.
Details
- Affected product:
- AlmaLinux 9.2 ESU , TuxCare 9.6 ESU , TuxCare 9.8 ESU
- Affected packages:
- perl-URI @ 5.09 (+2 more)