CVE-2025-4215 is a vulnerability identified in gorhill's uBlock Origin browser extension, specifically affecting versions up to 1.63.3b16. The issue resides in the function currentStateChanged within the src/js/1p-filters.js file, part of the UI component. The vulnerability is characterized by inefficient regular expression complexity, which can be exploited remotely. This means that crafted input can cause the regular expression engine to consume excessive CPU resources, potentially leading to performance degradation or denial of service conditions within the browser extension. The attack complexity is considered high, indicating that exploitation requires significant effort or expertise, and no authentication or privileges are needed. User interaction is required, as the CVSS vector indicates UI:P (user interaction required). The vulnerability does not impact confidentiality, integrity, or availability directly but can cause limited availability issues due to resource exhaustion. The vulnerability has been publicly disclosed, but no known exploits are currently observed in the wild. The issue is addressed by upgrading to version 1.63.3b17, which includes a patch identified by commit eaedaf5b10d2f7857c6b77fbf7d4a80681d4d46c. The CVSS 4.0 score is 2.3, reflecting a low severity level due to the limited impact and high exploitation complexity.

For European organizations, the impact of this vulnerability is relatively low but not negligible. uBlock Origin is a widely used open-source ad blocker and privacy extension, popular among privacy-conscious users and organizations aiming to reduce exposure to malicious ads and trackers. If exploited, the inefficient regular expression complexity could cause the extension to become unresponsive or slow, potentially degrading user experience and productivity. In environments where browser stability and performance are critical, such as financial institutions or government agencies, this could lead to minor disruptions. However, since the vulnerability does not allow for data leakage or privilege escalation, the direct risk to sensitive information or system integrity is minimal. The requirement for user interaction and the high complexity of exploitation further reduce the likelihood of widespread impact. Nevertheless, organizations that rely heavily on uBlock Origin for security and privacy should consider timely patching to maintain optimal protection and avoid any potential denial of service scenarios.

European organizations should implement the following specific mitigation steps: 1) Immediately upgrade all instances of uBlock Origin to version 1.63.3b17 or later to apply the official patch addressing this vulnerability. 2) Establish or reinforce policies to ensure browser extensions are kept up to date automatically or through managed updates, minimizing the window of exposure. 3) Educate users about the importance of applying updates promptly and exercising caution with unsolicited or suspicious web content that could trigger complex regular expressions. 4) Monitor browser performance metrics and logs for signs of unusual CPU usage or extension crashes that might indicate attempted exploitation. 5) Consider deploying endpoint security solutions capable of detecting anomalous browser behavior or resource exhaustion patterns. 6) For organizations with strict security requirements, evaluate alternative ad-blocking solutions with a lower attack surface or implement network-level ad filtering to reduce reliance on client-side extensions.