Angular is Vulnerable to XSRF Token Leakage via Protocol-Relative URLs in Angular HTTP Client

The vulnerability is a **Credential Leak by App Logic** that leads to the **unauthorized disclosure of the Cross-Site Request Forgery (XSRF) token** to an attacker-controlled domain. Angular's HttpClient has a built-in XSRF protection mechanism that works by checking if a request URL starts with a protocol (`http://` or `https://`) to determine if it is cross-origin. If the URL starts with protocol-relative URL (`//`), it is incorrectly treated as a same-origin request, and the XSRF token is automatically added to the `X-XSRF-TOKEN` header. ### Impact The token leakage completely bypasses Angular's built-in CSRF protection, allowing an attacker to capture the user's valid XSRF token. Once the token is obtained, the attacker can perform arbitrary Cross-Site Request Forgery (CSRF) attacks against the victim user's session. ### Attack Preconditions 1. The victim's Angular application must have **XSRF protection enabled**. 2. The attacker must be able to make the application send a state-changing HTTP request (e.g., `POST`) to a **protocol-relative URL** (e.g., `//attacker.com`) that they control. ### Patches - 19.2.16 - 20.3.14 - 21.0.1 ### Workarounds Developers should avoid using protocol-relative URLs (URLs starting with `//`) in HttpClient requests. All backend communication URLs should be hardcoded as relative paths (starting with a single `/`) or fully qualified, trusted absolute URLs.

Source published

26 Nov 2025 23:18:50 UTC

Source modified

10 Sep 2026 03:50:30 UTC

Observed here

24 Oct 2026 13:17:17 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V4 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:H/SI:N/SA:N

Publisher rating · HIGH