CVE-2025-6069: 
Python Interpreter vulnerability analysis and mitigation

CVE-2025-6069 affects the html.parser.HTMLParser class in Python, discovered and disclosed on June 13, 2025. The vulnerability exists in Python's standard library and affects multiple versions of Python. The issue was identified and reported by the Python Software Foundation (Python CVE, NVD CVE).

The vulnerability involves a worst-case quadratic complexity issue in the HTMLParser class when processing certain crafted malformed inputs. The CVSS v3.1 base score is 4.3 (MEDIUM), with a vector string of CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L. The issue specifically affects the processing of malformed HTML inputs, where the parser's behavior could lead to excessive processing time (Python Issue).

The vulnerability can potentially lead to amplified denial-of-service conditions. Test cases that previously took about an hour to process now take a fraction of a second after the fix, demonstrating the significant performance impact of the vulnerability (Python PR).

The issue has been fixed in multiple Python versions through a series of patches. The fix has been backported to Python versions 3.9 through 3.14. Users should update to the patched versions of Python to mitigate this vulnerability (Python Commits).