Overview
CVE-2025-12084 describes a potential denial-of-service (DoS) vulnerability in Python’s xml.dom.minidom module. Specifically, the vulnerability arises when constructing deeply nested XML documents using methods like appendChild(). The underlying algorithm responsible for managing element IDs (via _clear_id_cache()) exhibits quadratic complexity, meaning the time required to build the XML structure grows proportionally to the square of the depth of the nesting. This can lead to significant performance degradation and potentially crash the application when dealing with extremely nested documents.
Technical Details
The root cause of this vulnerability lies in the implementation of the internal _clear_id_cache() function, which is invoked when adding new elements to the XML document. This function is responsible for maintaining a cache of element IDs, and the algorithm used to update this cache becomes inefficient as the depth of the XML tree increases. The vulnerability manifests because appendChild(), which is frequently used when programmatically creating XML documents, triggers this cache update. The quadratic complexity stems from the need to potentially iterate through all existing elements when adding a new node, leading to a performance bottleneck with highly nested structures.
Consider this simplified scenario:
import xml.dom.minidom
doc = xml.dom.minidom.Document()
root = doc.createElement("root")
doc.appendChild(root)
parent = root
for i in range(1000): #Deep Nesting
child = doc.createElement(f"child_{i}")
parent.appendChild(child)
parent = child
While this code snippet is illustrative, the actual performance impact depends on the specific use case and the depth of nesting involved. The performance degradation becomes increasingly noticeable as the depth increases substantially.
CVSS Analysis
As of the publication date of this article, CVE-2025-12084 has not been assigned a CVSS score. This is likely because the vulnerability requires a specific usage pattern (building deeply nested XML documents) to be exploitable and doesn’t allow for direct code execution or information disclosure. The primary impact is availability degradation due to the excessive processing time.
Possible Impact
The primary impact of CVE-2025-12084 is a potential denial-of-service (DoS) vulnerability. An attacker could exploit this vulnerability by providing a specially crafted XML document, or a series of requests that triggers the creation of deeply nested XML structures. This would consume excessive CPU resources on the server, potentially leading to slow response times or even a complete service outage. Applications that rely on generating complex XML documents dynamically are most at risk.
Mitigation or Patch Steps
The recommended mitigation is to upgrade to a patched version of Python that includes the fix for this vulnerability. The fix, described in the references below, optimizes the ID cache management algorithm, significantly reducing the performance impact when building nested XML documents. Check for versions of python 3.x where this fix is included.
If upgrading Python is not immediately feasible, consider these alternative mitigation strategies:
- Limit XML Nesting Depth: Implement checks to restrict the maximum depth of XML documents that your application processes.
- Use Alternative XML Libraries: Consider using more performant XML libraries like
lxml, which may offer better performance for building complex XML structures. However, be sure to evaluate the security implications of switching libraries. - Input Validation: Carefully validate any XML input to ensure that it does not contain excessively deep nesting.
