CVE-2022-48565: Python plistlib XXE Vulnerability

CVE-2022-48565 Overview

An XML External Entity (XXE) vulnerability was discovered in Python through version 3.9.1, affecting the plistlib module. This module, used for parsing Apple property list (plist) files, accepted entity declarations in XML plist files, making it susceptible to XXE attacks. Successful exploitation could allow attackers to read arbitrary files, perform server-side request forgery (SSRF), or cause denial of service conditions on affected systems.

Critical Impact

Unauthenticated remote attackers can exploit this XXE vulnerability via network access to compromise confidentiality, integrity, and availability of systems running vulnerable Python versions.

Affected Products

• Python versions through 3.9.1
• Debian Linux 10.0
• Systems using the plistlib module for XML plist parsing

Discovery Timeline

• 2023-08-22 - CVE-2022-48565 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2022-48565

Vulnerability Analysis

The vulnerability exists in Python's plistlib module, which is used to read and write Apple plist files in XML format. The module's XML parser did not properly restrict the processing of external entity declarations within plist files. XML External Entity (XXE) attacks exploit this weakness by injecting malicious external entity references into XML documents.

When the plistlib module parses a specially crafted plist file containing external entity declarations, the XML parser resolves these entities, potentially allowing attackers to:

• Read sensitive files from the local filesystem (e.g., /etc/passwd, configuration files)
• Perform Server-Side Request Forgery (SSRF) by forcing the server to make HTTP requests to internal resources
• Cause denial of service through recursive entity expansion (billion laughs attack)
• Exfiltrate data to attacker-controlled servers

The vulnerability is classified as CWE-611 (Improper Restriction of XML External Entity Reference), indicating the core issue is insufficient validation of XML input containing entity declarations.

Root Cause

The root cause is the improper configuration of the underlying XML parser used by the plistlib module. By default, many XML parsers allow the processing of Document Type Definitions (DTDs) and external entity references. The plistlib module failed to disable these dangerous features when parsing plist XML files, allowing malicious entity declarations to be processed.

The fix involves configuring the XML parser to reject any entity declarations in XML plist files, effectively blocking XXE attack vectors at the parsing stage.

Attack Vector

The attack vector is network-based, requiring no authentication or user interaction. An attacker can exploit this vulnerability by:

1. Crafting a malicious plist file containing XXE payloads with external entity declarations
2. Delivering the malicious plist to a target application that uses Python's plistlib.load() or plistlib.loads() functions
3. When the application parses the plist, the XXE payload executes, potentially exposing sensitive data

Common attack scenarios include applications that accept user-uploaded plist files, process plist data from untrusted sources, or parse plist configurations from network endpoints.

Detection Methods for CVE-2022-48565

Indicators of Compromise

• Unusual file read operations targeting sensitive system files like /etc/passwd, /etc/shadow, or application configuration files
• Unexpected outbound network connections from Python processes to unknown external hosts
• Log entries showing XML parsing errors related to entity declarations or DTD processing
• Presence of plist files containing <!DOCTYPE> or <!ENTITY> declarations in uploaded or processed content

Detection Strategies

• Monitor Python application logs for XML parsing exceptions or warnings related to entity processing
• Implement network monitoring for SSRF indicators such as internal network reconnaissance from application servers
• Deploy file integrity monitoring on sensitive configuration files and system directories
• Use web application firewalls (WAF) configured to detect XXE payloads in incoming requests

Monitoring Recommendations

• Audit Python application dependencies and track usage of plistlib module across the environment
• Implement centralized logging for Python applications processing XML or plist content
• Configure alerts for unusual Python process behavior including excessive file read operations or network connections
• Review application code for instances of plistlib.load() and plistlib.loads() handling untrusted input

How to Mitigate CVE-2022-48565

Immediate Actions Required

• Upgrade Python to a patched version that addresses this vulnerability (versions after 3.9.1 with the security fix applied)
• Review all applications using the plistlib module for processing untrusted plist content
• Implement input validation to reject plist files containing DTD or entity declarations before parsing
• Consider using alternative plist parsing methods that enforce strict security controls

Patch Information

The vulnerability has been addressed in Python with changes to the plistlib module that no longer accept entity declarations in XML plist files. For detailed information about the fix, refer to the Python Bug Report #42051. Distribution-specific patches are available through:

• Debian LTS Advisory September 2023
• Debian LTS Advisory October 2023
• Fedora package announcements for affected Python versions
• NetApp Security Advisory NTAP-20231006-0007

Workarounds

• If upgrading is not immediately possible, implement application-level defenses by validating plist content before parsing
• Use the defusedxml library as a wrapper for XML parsing operations to automatically block XXE attacks
• Configure network segmentation to limit the impact of potential SSRF exploitation
• Restrict application permissions to minimize the impact of file disclosure attacks

# Verify Python version and check for vulnerable plistlib
python3 --version

# Install defusedxml as an additional protection layer
pip install defusedxml

# Check if your application uses plistlib
grep -r "import plistlib" /path/to/application/
grep -r "from plistlib" /path/to/application/