CVE-2026-46644
symfony/polyfill-intl-idn: xn-- labels with ASCII-only Punycode payloads are treated as equivalent to their decoded form
Impact
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 packages
| Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|
| composer | symfony/polyfill | >= 1.17.1, < 1.38.1 | 1.38.1 |
| composer | symfony/polyfill-intl-idn | >= 1.17.1, < 1.38.1 | 1.38.1 |
Weakness classification
References
- NVD record
- CVE.org record
- GitHub advisory
- https://github.com/advisories/GHSA-2xf4-cg6j-vhgq
- https://github.com/symfony/polyfill/security/advisories/GHSA-2xf4-cg6j-vhgq
- https://github.com/symfony/polyfill/commit/1be936e2491ccebe152bd736dfc91eb1422c8bec
- https://github.com/FriendsOfPHP/security-advisories/blob/master/symfony/polyfill-intl-idn/CVE-2026-46644.yaml
- https://github.com/FriendsOfPHP/security-advisories/blob/master/symfony/polyfill/CVE-2026-46644.yaml
- https://symfony.com/cve-2026-46644
- https://github.com/symfony/polyfill/releases/tag/v1.38.1