CVE-2025-6069 identifies a vulnerability in the Python Software Foundation's CPython interpreter, specifically within the html.parser.HTMLParser class. The root cause is an inefficient regular expression implementation that leads to quadratic time complexity when processing certain malformed HTML inputs. This inefficiency can be triggered by an attacker crafting malicious HTML content that causes the parser to consume excessive CPU cycles, resulting in an amplified denial-of-service (DoS) condition. The vulnerability affects CPython versions 3.10.0 through 3.14.0a1, including the initial 0 version, indicating a broad impact across recent and development releases. The CVSS 3.1 base score is 4.3 (medium severity), reflecting that exploitation requires network access and low privileges but no user interaction, and impacts availability only without compromising confidentiality or integrity. No known exploits have been reported in the wild to date. The vulnerability is categorized under CWE-1333, which relates to inefficient regular expression complexity leading to performance degradation. This issue is particularly relevant for applications and services that parse untrusted HTML data using CPython's html.parser module, as they may be susceptible to resource exhaustion attacks. The absence of patches at the time of reporting necessitates interim mitigations such as input validation, request rate limiting, and monitoring for abnormal CPU usage. Once patches are released by the Python Software Foundation, upgrading to fixed versions is critical to fully remediate the risk.

The primary impact of CVE-2025-6069 is the potential for denial-of-service attacks against applications using vulnerable CPython versions to parse HTML content. For European organizations, this could translate into service disruptions, degraded performance, or outages in web applications, APIs, or data processing systems that rely on the html.parser.HTMLParser class. Industries such as finance, healthcare, government, and critical infrastructure that utilize Python-based services may face operational risks if attackers exploit this vulnerability to overwhelm systems. Although the vulnerability does not affect confidentiality or integrity, availability impacts can lead to significant business interruptions and reputational damage. The medium CVSS score reflects moderate risk, but the ease of triggering the vulnerability with crafted inputs and no need for user interaction increases the threat surface. Organizations processing large volumes of untrusted HTML data or exposed to public networks are particularly vulnerable. The lack of known exploits currently reduces immediate risk but does not eliminate the potential for future attacks, especially as exploit techniques evolve.

To mitigate CVE-2025-6069, European organizations should prioritize the following actions: 1) Monitor the Python Software Foundation's releases closely and apply security patches or upgrade to fixed CPython versions as soon as they become available. 2) Implement strict input validation and sanitization on all HTML content before parsing to detect and reject malformed or suspicious inputs that could trigger the vulnerability. 3) Employ rate limiting and throttling on services that accept HTML input to reduce the risk of resource exhaustion from repeated malicious requests. 4) Use alternative HTML parsing libraries with better performance characteristics or known resistance to regular expression complexity issues, if feasible. 5) Monitor system CPU and memory usage for anomalies that may indicate exploitation attempts. 6) Conduct code reviews and security testing focused on HTML parsing components to identify and remediate potential abuse vectors. 7) Educate developers and security teams about the vulnerability and encourage secure coding practices around input handling. These targeted measures go beyond generic advice by focusing on the specific nature of the vulnerability and the affected component.