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CVE-2026-45071 – XXE Local File Disclosure – Symfony DomCrawler (symfony/dom-crawler < 5.4.52 / 6…

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Summary

CVE-2026-45071 is an XML External Entity (XXE) injection vulnerability in the Symfony symfony/dom-crawler component, affecting all supported Symfony branches prior to versions 5.4.52, 6.4.40, 7.4.12, and 8.0.12. The flaw enables unauthenticated, network-accessible attackers to supply malicious XML that causes the server to read and disclose arbitrary local files. It carries a CVSS 4.0 score of 8.7 (High) with no authentication and no user interaction required.

Technical details

  • Root cause: The Crawler::addXmlContent() method sets DOMDocument::$validateOnParse = true immediately before calling loadXML(). This assignment re-enables libxml’s DTD subset processing and external entity resolution, overriding the safe parsing state that Symfony otherwise maintains.
  • Why LIBXML_NONET is insufficient: Although LIBXML_NONET is passed to loadXML() to block network-based entity fetches, it does not prevent file:// URI entities from being resolved. An attacker can therefore supply a document with a SYSTEM "file:///etc/passwd" entity declaration (or any path readable by the web process) and receive its content in the server’s response.
  • Trigger condition: Exploitation requires an application to call Crawler::addXmlContent() with attacker-controlled XML in a web-reachable request handler. The method is not invoked automatically — it must be called explicitly in a controller or service that processes user-supplied XML (e.g., XML API endpoints, feed parsers, or file upload handlers). The symfony/browser-kit component (HttpBrowser) is also affected, as it invokes this method internally when parsing XML responses.
  • Attack vector: Network, no authentication, no user interaction (CVSS 4.0: AV:N/AC:L/AT:N/PR:N/UI:N).
  • Impact: Unauthorized disclosure of arbitrary local files readable by the application process, including configuration files, environment files, and application secrets. Confidentiality impact is rated High; integrity and availability are unaffected.

Affected software

  • symfony/dom-crawler and symfony/browser-kit all versions < 5.4.52
  • symfony/dom-crawler and symfony/browser-kit versions ≥ 6.0.0 and < 6.4.40
  • symfony/dom-crawler and symfony/browser-kit versions ≥ 7.0.0 and < 7.4.12
  • symfony/dom-crawler and symfony/browser-kit versions ≥ 8.0.0 and < 8.0.12

Severity

CVSS 4.0 Base Score: 8.7 (High)
Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N

Mitigation and recommended actions

  • Immediate action — upgrade to a patched release:
    • Symfony 5.x: upgrade to 5.4.52 or later
    • Symfony 6.x: upgrade to 6.4.40 or later
    • Symfony 7.x: upgrade to 7.4.12 or later
    • Symfony 8.x: upgrade to 8.0.12 or later
  • The fix removes the $dom->validateOnParse = true assignment from Crawler::addXmlContent(), ensuring external entity resolution remains disabled during XML parsing.
  • If immediate patching is not possible: Audit all application code for direct or indirect calls to Crawler::addXmlContent() — and any use of HttpBrowser to fetch XML responses — where the XML content originates from untrusted user input. As a temporary measure, implement validation that rejects XML payloads containing DTD declarations (<!DOCTYPE) at the application layer or WAF level.

IONIX Status

The IONIX research team is tracking ongoing exploitation attempts and recommends immediate patching. Potentially affected assets are outlined in this post.

References

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