What’s Vulnerable › Vulnerabilities

CVE-2026-46644: symfony/polyfill-intl-idn accepts xn-- labels whose Punycode payload decodes to ASCII-only: insecure equivalence

• Severity: medium (CVSS 6.9 v4.0)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.5% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-07-14 · updated 2026-07-15
• Weakness: CWE-1289

Description

Symfony 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.

Affected products

• symfony polyfill: from 1.17.1, < 1.38.1
• symfony polyfill-intl-idn: from 1.17.1, < 1.38.1

References

• https://github.com/symfony/polyfill/commit/1be936e2491ccebe152bd736dfc91eb1422c8bec
• https://github.com/symfony/polyfill/releases/tag/v1.38.1
• https://github.com/symfony/polyfill/security/advisories/GHSA-2xf4-cg6j-vhgq

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