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 1.3
The Security component in Symfony 2.0.x before 2.0.25, 2.1.x before 2.1.13, 2.2.x before 2.2.9, and 2.3.x before 2.3.6 allows remote attackers to cause a denial of service (CPU consumption) via a long password that triggers an expensive hash computation, as demonstrated by a PBKDF2 computation, a similar issue to CVE-2013-5750.