Bug 2526492 (CVE-2026-19953)

Summary:	CVE-2026-19953 URI: URI (for Perl): Security bypass due to incorrect hostname encoding via missing Unicode normalization
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security DevOps Team <prodsec-dev>
Status:	NEW ---	QA Contact:
Severity:	medium	Docs Contact:
Priority:	medium
Version:	unspecified	CC:	akhatavk, aos-team-art-private, asdas, dpaolell, jdelft, jupierce, lgarciaa, mbiarnes, ppalepu, ppostler, prdhamdh, rhel-process-autobot, sghai, sidsharm, suppawar, vlaad, watson-tool-maintainers, yguenane
Target Milestone:	---	Keywords:	Security
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
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Doc Text:	A flaw was found in the URI component for Perl. This vulnerability occurs because the `nameprep` function, responsible for encoding hostnames, does not properly normalize Unicode characters. As a result, a hostname that is not in a standard Unicode form (non-NFC) can be encoded into a non-standard label. This discrepancy can lead to a situation where security checks, such as allow lists or Server-Side Request Forgery (SSRF) filters, may incorrectly process hostnames, potentially allowing an attacker to bypass security restrictions.	Story Points:	---
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Documentation:	---	CRM:
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oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:

Description OSIDB Bzimport 2026-08-31 20:22:01 UTC

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.