Angular is a development platform for building mobile and desktop web applications using TypeScript/JavaScript and other languages. Prior to 20.3.34 and 21.0.3, the @angular/common HttpClient function xsrfInterceptorFn uses a regular expression that does not normalize request URLs in the same way as the browser's WHATWG URL parser. With XSRF protection enabled, a mutating HTTP request to an attacker-controlled URL containing backslashes, stripped control characters or spaces, or removable ASCII whitespace can be misclassified as relative and same-origin, causing the interceptor to attach the X-XSRF-TOKEN header before the browser dispatches the request to a cross-origin host. With permissive CORS handling for the custom header, the attacker can obtain the victim's XSRF token and use it to perform cross-site request forgery against the victim session. This issue is fixed in versions 20.3.34 and 21.0.3.