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How the Mentioned CVE Works (CVE-2025-12084)
This vulnerability exists in the `xml.dom.minidom` module of CPython, the standard Python implementation. The security flaw is rooted in an inefficient algorithm within the `_clear_id_cache()` function, which is called by methods like `appendChild()` when building or modifying XML Document Object Model (DOM) trees.
The algorithm exhibits quadratic time complexity (O(n²)). This means the processing time increases exponentially with the depth of the XML element nesting, not linearly. When an application parses or constructs an excessively and deeply nested XML document, this function must clear an internal ID cache repeatedly in an inefficient manner.
An attacker can exploit this by submitting a specially crafted XML payload with extreme levels of nesting. As the vulnerable Python code processes this document, the inefficient cache-clearing routine consumes disproportionate amounts of CPU resources. This leads to resource exhaustion, causing severe performance degradation or a complete denial of service (DoS) for the application. The attack vector is network-based, requires no privileges or user interaction, and directly impacts the availability of the service.
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Platform: Python (CPython)
Version: < 3.13.11
Vulnerability: Algorithmic Complexity DoS
Severity: Medium
Date: 2025-12-03
Prediction: 2025-12-17
What Undercode Say:
Check Python version
python3 --version
Find scripts using xml.dom.minidom
grep -r "import xml.dom.minidom" /path/to/code/
Test script to demonstrate nested XML (Conceptual)
cat > test_vulnerability.py << 'EOF'
import xml.dom.minidom
import sys
doc = xml.dom.minidom.Document()
parent = doc.createElement("root")
doc.appendChild(parent)
for i in range(int(sys.argv[bash])):
new_elem = doc.createElement("nested")
parent.appendChild(new_elem)
parent = new_elem
EOF
How Exploit:
An attacker crafts a malicious XML document with thousands or millions of nested elements. This document is sent to a vulnerable endpoint that processes XML using Python’s `xml.dom.minidom` parser, such as an API, web service, or data ingestion pipeline. Upon parsing, the quadratic complexity algorithm triggers, causing maximum CPU utilization, hanging the process, and denying service to legitimate users.
Protection from this CVE:
Apply official patches. For CPython versions 3.13, upgrade to >=3.13.11; for 3.14, upgrade to >=3.14.2; for 3.15 pre-releases, upgrade to >=3.15.0a3. Implement input validation to reject XML documents exceeding a defined maximum depth or size. Use alternative XML libraries (e.g., defusedxml, lxml) with robust parsing guards. Deploy web application firewalls (WAF) with XML payload inspection to block deeply nested structures.
Impact:
The primary impact is availability loss through resource exhaustion (Denial of Service). Affected systems experience severe performance degradation or become unresponsive, disrupting business operations. There is no impact on data confidentiality or integrity. The vulnerability is classified under CWE-407: Inefficient Algorithmic Complexity.
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Sources:
Reported By: nvd.nist.gov
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