Affected versions
Symfony versions <5.4.52, >=6, <6.4.40, >=7, <7.4.12, >=8, <8.0.12 of the Symfony DOM Crawler component are affected by this security issue.
The issue has been fixed in Symfony 5.4.52, 6.4.40, 7.4.12, 8.0.12.
Description
symfony/dom-crawler provides the Crawler class for navigating HTML/XML documents with CSS/XPath selectors; symfony/browser-kit's HttpBrowser uses it to parse fetched pages.
Crawler::addXmlContent() sets DOMDocument::$validateOnParse = true before calling loadXML(). Setting validateOnParse re-enables libxml's DTD subset processing, including external entity resolution, even though LIBXML_NONET is passed. LIBXML_NONET blocks network fetches but not file:// entities. An attacker-supplied XML document with a SYSTEM "file:///etc/passwd" entity is therefore expanded.
Resolution
The Crawler::addXmlContent method does not set the validateOnParse flag anymore.
The patch for this issue is available here for branch 5.4.
Credits
We would like to thank Claude Mythos Preview (via Project Glasswing) for reporting the issue and providing the fix.