undici 8.10.0 through 8.10.2 fails to include the origin in cache and request‑deduplication keys when the cache or deduplicate interceptor is composed directly onto a Client or Pool. The internal key falls back to an empty string, causing a cacheable or in‑flight response from one upstream origin to be returned for a request to a different, trusted origin when the method, path, and relevant headers match. This flaw permits cross‑origin information disclosure and persistent cache poisoning, and a demonstrator achieved a JWT authentication bypass by having attacker‑controlled tokens accepted as trusted without contacting the issuing origin.

Vulnerable versions are undici 8.10.0, 8.10.1, and 8.10.2. Applications that use an Agent that carries the origin in its dispatch options are not affected. The component affected is the undici HTTP/1.1 client library for Node.js.

The CVSS score of 7.4 indicates high impact. EPSS is not available, so the exploitation frequency cannot be quantified, but the vulnerability exists in multiple major releases and is not listed in CISA’s KEV catalog. The attack can be performed over arbitrary cross‑origin requests when interceptors are configured without origin isolation, enabling an attacker to serve poisoned cache entries or bypass authentication checks. The combination of high severity and ease of exploitation makes the risk significant for actively running services that rely on undici without origin protection.