symfony/polyfill-intl-idn accepts xn-- labels whose Punycode payload decodes to ASCII-only: insecure equivalence

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Summary

CVECVE-2026-46644
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-07-14 21:16:55 UTC
Updated2026-07-14 21:16:55 UTC
DescriptionSymfony Polyfill backports PHP features and provides compatibility layers for extensions and functions. From 1.17.1 until 1.38.1, symfony/polyfill-intl-idn accepts xn-- labels whose Punycode payload is empty or decodes to ASCII-only code points because Idn::process() does not enforce the UTS #46 revision 33 requirement that decoded ACE labels contain at least one non-ASCII code point. Originally unequal domain names can be regarded as equal, which can lead to blacklist bypassing, inconsistent URL parsing, and server-side request forgery in applications using the polyfill to canonicalise or compare hostnames. This issue is fixed in version 1.38.1.

Risk And Classification

Primary CVSS: v4.0 6.9 MEDIUM from [email protected]

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:L/SI:L/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Problem Types: CWE-1289 | CWE-1289 CWE-1289: Improper Validation of Unsafe Equivalence in Input

VersionSourceTypeScoreSeverityVector
4.0[email protected]Secondary6.9MEDIUMCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:L/SI:L/SA:N/E:X/C...
4.0CNADECLARED6.9MEDIUMCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:L/SI:L/SA:N

CVSS v4.0 Breakdown

Attack Vector
Network
Attack Complexity
Low
Attack Requirements
None
Privileges Required
None
User Interaction
None
Confidentiality
None
Integrity
Low
Availability
None
Sub Conf.
Low
Sub Integrity
Low
Sub Availability
None

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:L/SI:L/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Symfony Polyfill affected >= 1.17.1, < 1.38.1 Not specified
CNA Symfony Polyfill-intl-idn affected >= 1.17.1, < 1.38.1 Not specified

References

ReferenceSourceLinkTags
github.com/symfony/polyfill/commit/1be936e2491ccebe152bd736dfc91eb1422c8bec [email protected] github.com
github.com/symfony/polyfill/releases/tag/v1.38.1 [email protected] github.com
github.com/symfony/polyfill/security/advisories/GHSA-2xf4-cg6j-vhgq [email protected] github.com
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