Python HTMLParser Quadratic Complexity DoS Vulnerability
CVE-2025-6069 Published on June 17, 2025
HTMLParser quadratic complexity when processing malformed inputs
The html.parser.HTMLParser class had worse-case quadratic complexity when processing certain crafted malformed inputs potentially leading to amplified denial-of-service.
Vulnerability Analysis
CVE-2025-6069 can be exploited with network access, and requires small amount of user privileges. This vulnerability is considered to have a low attack complexity. The potential impact of an exploit of this vulnerability is considered to have no impact on confidentiality and integrity, and a small impact on availability.
Weakness Type
What is a ReDoS Vulnerability?
The product uses a regular expression with an inefficient, possibly exponential worst-case computational complexity that consumes excessive CPU cycles. Some regular expression engines have a feature called "backtracking". If the token cannot match, the engine "backtracks" to a position that may result in a different token that can match. Backtracking becomes a weakness if all of these conditions are met:
CVE-2025-6069 has been classified to as a ReDoS vulnerability or weakness.
Products Associated with CVE-2025-6069
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Affected Versions
Python Software Foundation CPython:- Before 3.9.24 is affected.
- Version 3.10.0 and below 3.10.19 is affected.
- Version 3.11.0 and below 3.11.14 is affected.
- Version 3.12.0 and below 3.12.12 is affected.
- Version 3.13.0 and below 3.13.6 is affected.
- Version 3.14.0a1 and below 3.14.0b3 is affected.
Exploit Probability
EPSS (Exploit Prediction Scoring System) scores estimate the probability that a vulnerability will be exploited in the wild within the next 30 days. The percentile shows you how this score compares to all other vulnerabilities.