urllib is an HTTP client for Node.js that supports authentication, redirects, timeouts, and other request features. Prior to 4.9.1 and 2.44.1, urllib follows redirects through followRedirect but reuses caller-supplied options across origins. In src/HttpClient.ts, #requestInternal recursively calls this.#requestInternal(nextUrl.href, options, requestContext), causing options.headers and auth or digestAuth values to be reused when the redirect target has a different scheme, host, or port. Authorization, Cookie, Proxy-Authorization, x-api-key, x-auth-token, and x-access-token can therefore be sent to an attacker-controlled redirected origin, exposing credentials intended for the original origin and potentially allowing reuse against the original partner API or related services. No user interaction is required. This issue is fixed in versions 2.44.1 and 4.9.1.

CVE-2026-55553 affects the urllib HTTP client library for Node.js, which incorrectly reuses caller-supplied options including authentication headers when following redirects across different origins. The vulnerability exists in src/HttpClient.ts where the #requestInternal function recursively passes the same options object to redirected requests regardless of scheme, host, or port changes. Sensitive headers such as Authorization, Cookie, Proxy-Authorization, x-api-key, x-auth-token, and x-access-token can be leaked to attacker-controlled redirect destinations. No user interaction is required for exploitation, making this a significant credential exposure risk. The issue affects urllib versions prior to 2.44.1 and 4.9.1. Fixes have been released in versions 2.44.1 and 4.9.1 via two separate commits. The vulnerability could allow attackers to harvest credentials and potentially reuse them against the original API or related services.