CVE-2025-6069 is a vulnerability identified in the Python Software Foundation's CPython implementation, specifically within the html.parser.HTMLParser class. The issue arises from inefficient regular expression handling that leads to worst-case quadratic time complexity when processing certain crafted malformed HTML inputs. This inefficiency can be exploited to cause an amplified denial-of-service (DoS) condition by forcing the parser to consume excessive CPU resources, thereby degrading or halting the availability of applications relying on this parser. The vulnerability affects CPython versions from the initial release up to 3.14.0a1. The nature of the flaw is tied to CWE-1333, which concerns inefficient regular expression complexity, a common source of algorithmic complexity vulnerabilities. The CVSS v3.1 base score is 4.3 (medium severity), with an attack vector of network (AV:N), low attack complexity (AC:L), requiring low privileges (PR:L), no user interaction (UI:N), unchanged scope (S:U), no impact on confidentiality or integrity (C:N/I:N), and limited impact on availability (A:L). No known exploits are currently reported in the wild, and no official patches have been linked yet. This vulnerability primarily threatens applications that parse untrusted or malformed HTML content using the vulnerable HTMLParser class, potentially allowing attackers to degrade service availability through resource exhaustion.

For European organizations, the impact of CVE-2025-6069 is primarily related to service availability. Organizations that utilize Python-based applications or services that parse HTML content—such as web scrapers, content management systems, web frameworks, or security tools—may be vulnerable to denial-of-service attacks if they process untrusted input using the affected HTMLParser class. This could lead to temporary service outages, degraded performance, or increased operational costs due to resource exhaustion. Sectors with high reliance on Python for web services, data processing, or automation—such as financial services, telecommunications, government agencies, and technology firms—may face operational disruptions. While the vulnerability does not compromise data confidentiality or integrity, the availability impact can affect business continuity and user trust. The requirement for low privileges to exploit means that even limited access attackers or remote threat actors could trigger the DoS condition if they can supply crafted HTML inputs. Given the widespread use of Python in Europe, the vulnerability could have broad implications if not mitigated promptly.

To mitigate CVE-2025-6069, European organizations should: 1) Identify and inventory all Python applications and services using the html.parser.HTMLParser class, especially those processing external or untrusted HTML content. 2) Apply updates or patches from the Python Software Foundation as soon as they become available, prioritizing upgrades beyond version 3.14.0a1 where the issue is resolved. 3) Implement input validation and sanitization to reject or sanitize malformed HTML inputs before parsing, reducing the risk of triggering the inefficient regex processing. 4) Consider using alternative HTML parsing libraries that are not vulnerable to this inefficiency, such as lxml or BeautifulSoup with different parsers, for untrusted input. 5) Employ resource limiting techniques such as CPU and memory usage caps, timeouts, or sandboxing for processes that parse HTML to contain potential DoS impacts. 6) Monitor application performance and logs for unusual CPU spikes or slowdowns during HTML parsing operations, which may indicate exploitation attempts. 7) Educate developers and security teams about the risks of algorithmic complexity vulnerabilities and encourage secure coding practices around input handling and parsing.