Encode URI up to 5.35 Nameprep host server-side request forgery

Summaryinfo

A vulnerability categorized as critical has been discovered in Encode URI up to 5.35. Affected by this issue is the function host of the component Nameprep. The manipulation results in server-side request forgery. This vulnerability was named CVE-2026-19953. The attack may be performed from remote. There is no available exploit.

Detailsinfo

A vulnerability, which was classified as critical, was found in Encode URI up to 5.35. Affected is the function host of the component Nameprep. The manipulation with an unknown input leads to a server-side request forgery vulnerability. CWE is classifying the issue as CWE-918. The web server receives a URL or similar request from an upstream component and retrieves the contents of this URL, but it does not sufficiently ensure that the request is being sent to the expected destination. This is going to have an impact on confidentiality, integrity, and availability. CVE summarizes:

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.

The advisory is available at github.com. This vulnerability is traded as CVE-2026-19953 since 08/15/2026. The exploitability is told to be easy. It is possible to launch the attack remotely. Technical details are known, but there is no available exploit.

Upgrading to version 5.36 eliminates this vulnerability.

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Productinfo

Vendor

• Encode

Name

• URI

Version

• 5.0
• 5.1
• 5.2
• 5.3
• 5.4
• 5.5
• 5.6
• 5.7
• 5.8
• 5.9
• 5.10
• 5.11
• 5.12
• 5.13
• 5.14
• 5.15
• 5.16
• 5.17
• 5.18
• 5.19
• 5.20
• 5.21
• 5.22
• 5.23
• 5.24
• 5.25
• 5.26
• 5.27
• 5.28
• 5.29
• 5.30
• 5.31
• 5.32
• 5.33
• 5.34
• 5.35

CPE 2.3info

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CPE 2.2info

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