CVE-2026-91184: NGINX Gateway Fabric vulnerability
Description
NGINX Gateway Fabric has a vulnerability when it renders the spec.basic.realm (and spec.jwt.realm) field of a namespaced AuthenticationFilter verbatim, unescaped and unvalidated, into the shared data-plane nginx.conf as authbasic "<realm>";. A namespaced authenticated attacker that configures AuthenticationFilter CRD to an HTTPRoute/GRPCRoute on a shared Gateway can craft a realm value that closes the quoted directive and the enclosing location {} block and injects arbitrary NGINX directives into that Gateway's data-plane config.
Impact
A remote authenticated attacker can send crafted requests to configure NGINX Gateway Fabric AuthenticationFilter CRD and may be able to read every co-located tenant's mounted secrets, SSRF via proxypass, reading the pod ServiceAccount token, or hijacking other tenants' routes. There is no data plane exposure; this is a control plane issue only.
Note: Software versions which have reached End of Technical Support (EoTS) are not evaluated.
Affected Software
Event History
Frequently Asked Questions
Who can exploit this issue?
An attacker needs authenticated, namespaced access that allows them to configure an AuthenticationFilter CRD and attach it to an HTTPRoute or GRPCRoute on a shared Gateway. It is a control-plane issue; unauthenticated data-plane access alone is not sufficient.
Are shared Gateway deployments at particular risk?
Yes. A malicious realm value can inject NGINX directives into the shared Gateway data-plane configuration, potentially affecting co-located tenants. The described impacts include access to mounted secrets, ServiceAccount tokens, SSRF through proxy_pass, and route hijacking.
Which configuration fields are relevant when assessing exposure?
Assess AuthenticationFilter resources using spec.basic.realm or spec.jwt.realm, especially where those resources can be attached to routes on a shared Gateway. The vulnerable behavior occurs because these realm values are rendered verbatim into nginx.conf without escaping or validation.
Does this vulnerability expose the data plane directly to remote unauthenticated attackers?
No. The advisory states that there is no data-plane exposure; exploitation requires control-plane access by an authenticated attacker.