CVE-2025-4690: 
Linux Debian vulnerability analysis and mitigation

CVE-2025-4690 is a Regular Expression Denial of Service (ReDoS) vulnerability in the linky filter of AngularJS's ngSanitize module. The vulnerability affects all versions of AngularJS, which is now End-of-Life and will not receive patches. It was published on August 19, 2025, with the CVE assigned by HeroDevs. The CVSS v3.1 base score is 4.3 (Medium) (Red Hat Advisory, HeroDevs Blog).

The root cause is classified as CWE-1333 (Inefficient Regular Expression Complexity). The linky filter uses a regular expression to detect URLs in input text; this regex is susceptible to super-linear (exponential) backtracking when processing specially crafted input strings. An attacker who can supply input to a field processed by the linky filter can trigger catastrophic backtracking in the JavaScript regex engine, causing the application's event loop to stall. No authentication is required, but user interaction (e.g., submitting crafted input) is needed to trigger the vulnerable code path (HeroDevs Blog, EUVD). A proof-of-concept demonstrating the issue is publicly available via CodePen (HeroDevs PoC).

Successful exploitation causes a temporary denial of service by blocking the JavaScript event loop on the server or client rendering the affected page, resulting in low availability impact with no confidentiality or integrity loss. The scope is limited to the affected application instance; lateral movement is not a direct consequence of this vulnerability. Applications that expose user-controlled input to the linky filter — such as comment fields, messaging features, or any text rendered through ngSanitize — are at risk of becoming unresponsive under attack (Red Hat Advisory, HeroDevs Blog).

A public proof-of-concept is available on CodePen (HeroDevs PoC). There is no evidence of in-the-wild exploitation or threat actor attribution at this time. The EPSS score is approximately 0.015% (0.000150), indicating a very low probability of exploitation in the near term. The vulnerability is not listed in the CISA Known Exploited Vulnerabilities (KEV) catalog. Detection is available via Nessus plugin 278624 (Tenable).

1. Identify target: Locate a web application using AngularJS's ngSanitize module with the linky filter applied to user-controlled input (e.g., a comment box, bio field, or messaging feature).
2. Craft malicious input: Construct a large string designed to trigger catastrophic backtracking in the linky filter's URL-detection regex — for example, a long sequence of characters that partially matches URL patterns but forces repeated backtracking (see the public PoC for a working example).
3. Submit the payload: Submit the crafted string through the vulnerable input field. No authentication is required; the input only needs to reach the linky filter processing path.
4. Trigger ReDoS: The regex engine enters super-linear backtracking, consuming excessive CPU time and blocking the JavaScript event loop, causing the application to become unresponsive or significantly degraded for the duration of processing (HeroDevs Blog, HeroDevs PoC).

• Logs: Sudden spike in request processing time or timeouts for endpoints that render user-supplied text through the linky filter; application error logs showing event loop blocking or unresponsive state.
• Process: Abnormally high CPU utilization by the Node.js or browser process rendering the AngularJS application, sustained for an unusual duration after receiving specific input.
• Network: Repeated submissions of unusually long strings (hundreds to thousands of characters) to input fields on AngularJS-powered pages, particularly from a single source IP.

Since AngularJS is End-of-Life, no official patch will be released for this vulnerability. The primary recommended remediation is to migrate away from AngularJS to a supported framework (e.g., Angular). As an interim measure, HeroDevs offers Never-Ending Support (NES) for AngularJS, which provides patched versions for organizations unable to migrate immediately (HeroDevs Advisory). Additionally, developers should avoid passing untrusted user input to the linky filter, or implement server-side input length limits and sanitization to prevent excessively long strings from reaching the vulnerable regex (Red Hat Advisory).

HeroDevs, the CVE assigner, published a detailed blog post and PoC demonstrating the vulnerability and promoted it via their official Twitter/X account (HeroDevs Blog, HeroDevs X). Red Hat acknowledged the vulnerability in their security advisory portal (Red Hat Advisory). Community discussion appeared on Reddit's OSS EOL subreddit, reflecting broader concerns about the risks of continuing to use End-of-Life frameworks (Reddit).