CVE-2026-46644: Symfony Polyfill

Medium severity, CVSS 6.9. EPSS: 0.5% chance of exploitation in the next 30 days.

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, before 1.38.1 (fixed in 1.38.1)
• Symfony Polyfill-Intl-Idn: from 1.17.1, before 1.38.1 (fixed in 1.38.1)

Published 2026-07-14. Last modified 2026-07-15.