CVE-2025-45526 is a denial of service (DoS) vulnerability affecting the JavaScript library microlight, specifically version 0.0.7. Microlight is a client-side syntax highlighting library that processes textual content within HTML elements marked with the 'microlight' class. The vulnerability arises because the library does not impose any limits on the size of the textual content it processes. When an attacker supplies an excessively large input—on the order of 100 million characters—the reset function within microlight.js triggers excessive consumption of CPU and memory resources. This resource exhaustion leads to browser crashes or causes the browser to become unresponsive, effectively resulting in a denial of service condition for the end user. Exploitation requires an attacker to lure a user into visiting a malicious webpage containing a microlight element with the large payload. Since the vulnerability is client-side and triggered by user interaction (visiting a crafted webpage), it does not require authentication but does require user action. There are no known exploits in the wild at the time of publication, and no patches or updates have been released yet. The vulnerability does not affect server-side components but targets the client environment, impacting availability by crashing or freezing browsers. The lack of input size validation in the library's reset function is the root cause, and the vulnerability is specific to the microlight library's handling of large content within the DOM.

For European organizations, the primary impact of this vulnerability is on the availability of web applications or internal tools that utilize the microlight library for syntax highlighting. Organizations that embed microlight in their web portals, developer tools, or documentation platforms may experience browser crashes or unresponsiveness when users access pages with maliciously crafted content. This can disrupt business operations, reduce productivity, and degrade user experience. While the vulnerability does not directly compromise confidentiality or integrity, the denial of service could be leveraged as part of a broader attack chain to distract or disrupt users. Sectors with high reliance on web-based developer environments, such as software companies, financial institutions with internal coding tools, and public sector entities providing online documentation, are particularly at risk. Additionally, the vulnerability could be exploited in targeted phishing campaigns to disrupt key personnel's access to critical web resources. The impact is limited to client-side environments and requires user interaction, which somewhat reduces the attack surface but does not eliminate risk, especially in environments with less stringent web browsing policies.

To mitigate this vulnerability, European organizations should take the following specific actions: 1) Identify and inventory all web applications and internal tools that use the microlight library, particularly version 0.0.7 or earlier. 2) Temporarily disable or remove the microlight library from critical web pages until a patched version is available. 3) Implement client-side input size restrictions or sanitization to prevent rendering of excessively large content within microlight elements. 4) Employ Content Security Policy (CSP) headers to restrict loading of untrusted scripts and reduce the risk of malicious content injection. 5) Educate users about the risks of visiting untrusted or suspicious web pages, emphasizing caution with links received via email or messaging platforms. 6) Monitor web traffic and logs for unusual spikes in resource usage or repeated crashes that may indicate exploitation attempts. 7) Engage with the microlight library maintainers or community to track patch releases and apply updates promptly once available. 8) Consider alternative syntax highlighting libraries with better input validation and resource management if microlight usage is widespread and cannot be immediately patched.