Outdated JavaScript Framework Can Be Used to Slow Down Your Web App

Vulnerability Explanation

AngularJS versions 1.4.9 through 1.8.3 use an inefficient regular expression in the input[url] directive's URL validation logic. When a user submits a carefully crafted string — such as a very long, malformed URL — the regex engine enters catastrophic backtracking: the number of steps required to evaluate the expression grows exponentially with input length. This can monopolize the JavaScript event loop (client-side) or server-side processing time, causing the application to become unresponsive. A public proof-of-concept exists on StackBlitz, confirming the vulnerability is reproducible.

Root Cause

The URL validation regex used by AngularJS's input[url] directive is vulnerable to catastrophic backtracking due to ambiguous quantifiers (nested repetition groups). When the regex engine fails to match a crafted input, it exhaustively explores an exponential number of alternative paths before giving up, consuming excessive CPU time.

Technical Impact

An unauthenticated attacker can submit a crafted URL string to any form field using AngularJS's `<input type="url">` directive and cause the JavaScript thread to stall. In browser-side rendering this degrades the user's session; if URL validation is also performed server-side (e.g., via Node.js with AngularJS SSR or shared validation logic), it can cause a denial-of-service condition affecting all users. CVSS 3.1: AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L — CVSS score 5.3 (Medium).

Severity Justification

CVSS 3.1 score of 5.3 (Medium). Network-accessible, no authentication required, no privileges needed, but impact is limited to availability (low) with no confidentiality or integrity impact. A public PoC exists, but real-world exploitation requires targeting a specific input element type.

Affected Components

• AngularJS (angular) >= 1.4.9, < 1.8.4

Remediation Steps

1. Upgrade AngularJS to a patched version. The official community patch is available in version 1.8.4+ via third-party extended support providers (HeroDevs NES or TuxCare ELS), as AngularJS 1.x reached end-of-life on December 31, 2021 and no official npm release beyond 1.8.3 exists.
2. If upgrading is not immediately possible, audit your templates for all `<input type="url">` elements that use AngularJS's built-in URL validation (i.e., use `ng-model` without a custom validator override).
3. As a short-term mitigation, add a `maxlength` attribute to all `<input type="url">` fields to limit the length of user-supplied input and reduce the attack surface for catastrophic backtracking.
4. If server-side URL validation is performed using the same AngularJS regex pattern, replace it with a safe alternative such as the WHATWG URL API (`new URL(input)`) or a well-tested, linear-time regex library.
5. Plan and begin migration away from AngularJS to a supported framework (Angular 2+, React, or Vue). AngularJS is EOL and will continue to accumulate unpatched CVEs.

Verification Steps

1. Run `npm list angular` or check your `package.json` to confirm the installed version of AngularJS.
2. After upgrading, verify the new version is active by checking `angular.version` in the browser console — it should report 1.8.4 or higher.
3. Test the fix by submitting a long, malformed URL string (e.g., 100+ repeated characters with special patterns) into any `<input type="url">` field and confirm the page remains responsive.
4. Run a dependency audit with `npm audit` to confirm CVE-2023-26118 is no longer flagged.

Best Practices

• Add `maxlength` constraints to all user-facing input fields as a defense-in-depth measure against ReDoS and other input-length-dependent attacks.
• Avoid relying solely on client-side framework validation for URL or pattern inputs — always validate and sanitize on the server side using safe, linear-time methods.
• Maintain a software bill of materials (SBOM) and regularly audit third-party JavaScript dependencies for known CVEs using tools like `npm audit` or Snyk.
• Prioritize migration away from end-of-life frameworks; EOL software accumulates unpatched vulnerabilities over time, increasing risk with each passing month.