F5 NGINX Gateway Fabric up to 2.7.x AuthenticationFilter nginx.conf realm code injection

Summaryinfo

A vulnerability, which was classified as problematic, has been found in F5 NGINX Gateway Fabric up to 2.7.x. The affected element is an unknown function of the file nginx.conf of the component AuthenticationFilter. Performing a manipulation of the argument realm results in code injection. This vulnerability is identified as CVE-2026-91184. The attack can be initiated remotely. There is not any exploit available. It is advisable to upgrade the affected component.

Detailsinfo

A vulnerability classified as problematic has been found in F5 NGINX Gateway Fabric up to 2.7.x. This affects an unknown functionality of the file nginx.conf of the component AuthenticationFilter. The manipulation of the argument realm with an unknown input leads to a code injection vulnerability. CWE is classifying the issue as CWE-94. The product constructs all or part of a code segment using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the syntax or behavior of the intended code segment. This is going to have an impact on confidentiality, integrity, and availability. The summary by CVE is:

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 auth_basic "<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 proxy_pass, 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.

It is possible to read the advisory at my.f5.com. This vulnerability is uniquely identified as CVE-2026-91184 since 09/30/2026. The exploitability is told to be easy. It is possible to initiate the attack remotely. The exploitation needs additional levels of successful authentication. Technical details of the vulnerability are known, but there is no available exploit. The pricing for an exploit might be around USD $0-$5k at the moment (estimation calculated on 10/14/2026). The attack technique deployed by this issue is T1059 according to MITRE ATT&CK.

Upgrading to version 2.8.0 eliminates this vulnerability.

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Productinfo

Type

• Web Server

Vendor

• F5

Name

• NGINX Gateway Fabric

Version

• 2.0
• 2.1
• 2.2
• 2.3
• 2.4
• 2.5
• 2.6
• 2.7

License

• commercial

Website

• Vendor: https://f5.com/

CPE 2.3info

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CPE 2.2info

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