CVE-2026-50107 Overview
CVE-2026-50107 is a configuration injection vulnerability in the NGINX configuration generator component of NGINX Gateway Fabric. When NGINX Plus or NGINX Open Source operates as the data plane for NGINX Gateway Fabric, user-supplied strings from the NginxProxy Custom Resource Definition (CRD) access log format setting are written directly into NGINX configuration templates. The generator does not sanitize or escape these values. An authenticated attacker with permissions to create or modify the affected CRDs can inject arbitrary NGINX configuration directives. The flaw is classified as Improper Neutralization of Special Elements in Output (CWE-74). This is a control plane issue, and the vulnerability trigger itself does not expose the data plane.
Critical Impact
An authenticated Kubernetes user with rights to modify the NginxProxy CRD can inject arbitrary NGINX directives into generated configuration, compromising the confidentiality and integrity of the control plane.
Affected Products
- NGINX Gateway Fabric using NGINX Plus as the data plane
- NGINX Gateway Fabric using NGINX Open Source as the data plane
- Software versions that have reached End of Technical Support (EoTS) are not evaluated by the vendor
Discovery Timeline
- 2026-06-17 - CVE-2026-50107 published to NVD
- 2026-06-17 - Last updated in NVD database
Technical Details for CVE-2026-50107
Vulnerability Analysis
NGINX Gateway Fabric uses a configuration generator to render NGINX directives based on Kubernetes Gateway API resources and custom resources. The NginxProxy CRD exposes an access log format setting that accepts user-controlled string values. The generator interpolates these values into NGINX configuration templates without applying input sanitization or output escaping. An authenticated attacker with sufficient Role-Based Access Control (RBAC) permissions to create or modify the NginxProxy CRD can supply crafted strings that break out of the access log format directive and introduce additional configuration directives. Because the generated configuration is then loaded by the NGINX data plane, the attacker can influence routing, logging, authentication, and other directive-controlled behavior on the control plane side.
Root Cause
The root cause is missing neutralization of special characters in the access log format field of the NginxProxy CRD. The configuration generator treats CRD field input as trusted template data instead of untrusted user input. This violates the CWE-74 principle of separating control planes from data planes during template rendering.
Attack Vector
The attack requires network access to the Kubernetes API and authenticated credentials with permission to write to NginxProxy resources. The attacker submits a crafted access log format string containing NGINX directive delimiters and arbitrary directives. When the configuration generator processes the resource, the injected directives are written into the rendered NGINX configuration and applied by the data plane. No user interaction is required. Refer to the F5 Security Article K000161785 for vendor-specific exploitation details.
Detection Methods for CVE-2026-50107
Indicators of Compromise
- Unexpected modifications to NginxProxy CRDs, particularly fields controlling the access log format
- Rendered NGINX configuration files containing directives not declared by Gateway API resources
- Kubernetes audit log entries showing create or update operations on NginxProxy resources from unusual service accounts or users
- NGINX reload events correlated with recent CRD changes from non-administrative principals
Detection Strategies
- Enable Kubernetes API audit logging for the gateway.nginx.org API group and alert on writes to NginxProxy resources.
- Diff generated NGINX configuration against the expected output from Gateway API resources to surface unauthorized directives.
- Apply admission control policies that validate the accessLog.format field against an allow-list of characters and tokens.
Monitoring Recommendations
- Monitor RBAC bindings that grant write access to NginxProxy and review them against least-privilege expectations.
- Track NGINX worker process reloads and correlate them with CRD modification events to identify suspicious sequences.
- Forward Kubernetes audit logs and NGINX Gateway Fabric controller logs to a centralized analytics platform for retention and query.
How to Mitigate CVE-2026-50107
Immediate Actions Required
- Restrict write permissions on NginxProxy CRDs to a minimal set of trusted cluster administrators using Kubernetes RBAC.
- Review existing NginxProxy resources for unexpected content in the access log format field and revert any unauthorized changes.
- Apply the fixed version of NGINX Gateway Fabric as referenced in the F5 Security Article K000161785.
- Rotate credentials for any service accounts that had write access to the affected CRDs prior to remediation.
Patch Information
F5 publishes fixed versions and remediation guidance in F5 Security Article K000161785. Upgrade NGINX Gateway Fabric to a version that sanitizes user-supplied template input. Versions in End of Technical Support are not evaluated and should be replaced with a supported release.
Workarounds
- Use a ValidatingAdmissionPolicy or third-party admission controller to reject NginxProxy resources whose accessLog.format contains characters used to terminate or introduce NGINX directives such as ;, {, or }.
- Limit the gateway.nginx.org API group permissions in RBAC roles to a dedicated platform team and remove broad cluster-admin access where feasible.
- Implement GitOps-driven configuration so that all NginxProxy changes pass through code review and signed commits before reaching the cluster.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
