Unsanitized input in XML External Entity

• Rule ID: ruby_lang_xml_external_entity_vulnerability
• Languages: ruby
• Source: xml_external_entity_vulnerability.yml

Description

Avoid parsing untrusted data as XML. Such data could include URIs that resolve to resources that are outside of the current context, leading to XML External Entity (XXE) injection.

Remediations

• Do disable external entity expansion in REXML before parsing any XML from untrusted sources. Set the REXML::Security.entity_expansion_text_limit to 0.

  REXML::Security.entity_expansion_text_limit = 0 # prevent REXML from expanding any text entities
  
  def parse_xml(raw_xml)
    begin
      return REXML::Document.new(raw_xml)
    rescue REXML::ParseException => e
      # handle error
    end
  end

• Do not allow REXML to expand text entities from untrusted input. This is the primary mechanism attackers use to perform XXE attacks. Avoid parsing XML without first disabling entity expansion.

  def unsafe_parse_xml(raw_xml)
    return REXML::Document.new(raw_xml) # unsafe
  end

References

• OWASP XML External Entity (XXE) prevention cheat sheet

Associated CWE

• CWE-611: Improper Restriction of XML External Entity Reference

OWASP Top 10

• A05:2021 - Security Misconfiguration

Configuration

To skip this rule during a scan, use the following flag

bearer scan /path/to/your-project/ --skip-rule=ruby_lang_xml_external_entity_vulnerability

To run only this rule during a scan, use the following flag

bearer scan /path/to/your-project/ --only-rule=ruby_lang_xml_external_entity_vulnerability