CVE-2026-49998 Details

A vulnerability in Centrifugo's dynamic JWKS endpoint verification can lead to cross-issuer JWT authentication bypass. This issue affects Centrifugo versions through 6.8.0. The vulnerability arises because the JWKS cache and singleflight lookup are only keyed by the JWT header 'kid', not by the resolved JWKS endpoint or issuer. As a result, a key cached from one issuer can be used to verify a token for another issuer, if both keys share the same 'kid' value and the first key is cached prior to the verification. This flaw is particularly relevant in multi-tenant deployments that use dynamic JWKS endpoints based on 'iss' or 'aud' claims, allowing an attacker to authenticate as a user in a different issuer/tenant namespace.

Users should update to Centrifugo version 6.8.1, which patches the vulnerability by scoping JWKS cache entries and singleflight keys to the resolved JWKS trust domain, rather than just the JWT 'kid'. For deployments that use dynamic JWKS endpoints, it's important to compute the endpoint namespace before cache lookup and to use a composite cache key that includes the resolved JWKS URL and the 'kid', ensuring that keys are cached and retrieved in a way that respects the boundaries of each issuer or tenant.