🚨 REXML denial of service vulnerability

Impact

The REXML gem before 3.3.6 has a DoS vulnerability when it parses an XML that has many deep elements that have same local name attributes.

If you need to parse untrusted XMLs with tree parser API like REXML::Document.new, you may be impacted to this vulnerability. If you use other parser APIs such as stream parser API and SAX2 parser API, this vulnerability is not affected.

Patches

The REXML gem 3.3.6 or later include the patch to fix the vulnerability.

Workarounds

Don't parse untrusted XMLs with tree parser API.

3.3.6

Improvements

• Removed duplicated entity expansions for performance.

  • GH-194
  • Patch by Viktor Ivarsson.

• Improved namespace conflicted attribute check performance. It was
  too slow for deep elements.

  • Reported by l33thaxor.

Fixes

• Fixed a bug that default entity expansions are counted for
  security check. Default entity expansions should not be counted
  because they don't have a security risk.

  • GH-198
  • GH-199
  • Patch Viktor Ivarsson

• Fixed a parser bug that parameter entity references in internal
  subsets are expanded. It's not allowed in the XML specification.

  • GH-191
  • Patch by NAITOH Jun.

• Fixed a stream parser bug that user-defined entity references in
  text aren't expanded.

  • GH-200
  • Patch by NAITOH Jun.

Thanks

• Viktor Ivarsson

• NAITOH Jun

• l33thaxor

3.3.5

Fixes

• Fixed a bug that REXML::Security.entity_expansion_text_limit
  check has wrong text size calculation in SAX and pull parsers.
  • GH-193
  • GH-195
  • Reported by Viktor Ivarsson.
  • Patch by NAITOH Jun.

Thanks

• Viktor Ivarsson

• NAITOH Jun

Does any of this look wrong? Please let us know.

See the full diff on Github. The new version differs by 18 commits:

• Add 3.3.6 entry
• parser tree: improve namespace conflicted attribute check performance
• Fix a bug that Stream parser doesn't expand the user-defined entity references for "text" (#200)
• parser: keep the current namespaces instead of stack of Set
• parser: move duplicated end tag check to BaseParser
• test tree-parser: move common method to base class
• test: fix indent
• test: fix indent
• Use loop instead of recursive call for Element#namespace
• Use loop instead of recursive call for Element#root
• test: split duplicated attribute case and namespace conflict case
• Fix to not allow parameter entity references at internal subsets (#191)
• Fix RuntimeError in `REXML::Parsers::BaseParser` for valid feeds (#199)
• Improve `BaseParser#unnormalize` (#194)
• Bump version
• Add 3.3.5 entry
• Fix calculation of Security.entity_expansion_text_limit in SAX/pull parsers (#195)
• Bump version

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