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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

Quick assessment

Affected
CVE-2026-19953
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

在 Perl 的 URI 模块 5.36 版本之前，对于非 NFC 形式的主机名，由于 nameprep 中缺少规范化步骤，会被编码为非标准的 Punycode 标签。 nameprep 虽然会对每个主机标签进行小写化，但不执行 Unicode 规范化。IDNA 要求标签在编码前必须规范化为形式 C（RFC 5891）。因此，若标签本身已处于 NFC 形式，其编码结果与经过 NFC 规范化后的编码结果不一致。例如，由预组合的 Devanagari 序列 U+0958 U+093E 构成的标签，在未规范化时编码为 ，

AI Predicted 5.3 Difficulty: Moderate

I. Basic Information for CVE-2026-19953

Vulnerability Information
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Vulnerability Title
URI versions before 5.36 for Perl encode non-NFC host names to non-standard punycode labels via missing normalization in nameprep
Source: CVE Program / CVE List V5
Vulnerability Description
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.
Source: CVE Program / CVE List V5
CVSS Information
N/A
Source: CVE Program / CVE List V5
Vulnerability Type
CWE-1289
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
- - 0 ~ 5.36 -

II. Public POCs for CVE-2026-19953

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III. Intelligence Information for CVE-2026-19953

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Patches & Fixes for CVE-2026-19953 (2)

IV. Related Vulnerabilities

Same weakness: CWE-1289

V. Comments for CVE-2026-19953

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