The vulnerability resides in Auth0 PHP SDK versions 8.0.0 up to 8.18.x where the cookies used for session tracking are encrypted with a key that lacks sufficient entropy. This weakness permits an attacker to launch a brute‑force attack on the encryption key, which in turn enables the attacker to forge valid session cookies. With a forged cookie the attacker can impersonate a legitimate user, gaining full authentication privileges and potentially accessing sensitive data.

Affected applications are those that incorporate Auth0’s PHP SDK, specifically Auth0‑PHP from version 8.0.0 through 8.18.x. The vulnerability is tied to the auth0:auth0-PHP product family and impacts any PHP‑based web service that relies on the SDK for authentication or session management.

The CVSS score of 8.2 indicates high severity, while the EPSS score of less than 1% suggests a low probability of widespread exploitation at the moment. Because the weakness involves cryptographic key entropy, an attacker needs to execute a brute‑force attack against the encryption key; however, once the key is recovered, forging a session cookie is straightforward. The absence of a CISA KEV listing and the specific nature of the flaw point to a targeted rather than mass exploitation scenario.