XML External Entity (XXE) Attack
An attack exploiting vulnerable XML parsers to access restricted files or execute remote code.
Understanding XXE Attacks
XML External Entity (XXE) attacks exploit vulnerabilities in XML parsers that process external entities. Attackers manipulate XML input to read sensitive files, execute code, or launch denial-of-service (DoS) attacks. This often occurs when applications allow user-controlled XML without proper security measures.
Common Methods of XXE Attacks
File Disclosure
Attackers use external entity references to read sensitive server files.
Example:
xml
CopyEdit
<!DOCTYPE foo [<!ENTITY xxe SYSTEM "file:///etc/passwd">]>
<foo>&xxe;</foo>
Server-Side Request Forgery (SSRF)
Malicious XML requests force the server to interact with internal systems.
Denial-of-Service (Billion Laughs Attack)
Recursive entity expansion overloads server resources.
Prevention and Mitigation Strategies
Disable External Entity Processing in XML parsers (
disableDTDin modern libraries).Use Secure XML Parsers that restrict entity expansion.
Sanitize Input to prevent malicious XML payloads.
Implement Whitelisting to restrict allowable input formats.