CVE-2026-50107: NGINX Gateway Fabric Configuration Injection Vulnerability

Technical summary

The vulnerability exists in NGINX Gateway Fabric's configuration generator, which templates NGINX configuration from Kubernetes Custom Resource Definitions (CRDs). The NginxProxy CRD's access_log format field accepts user input that is rendered directly into NGINX configuration templates without escaping or sanitization. An authenticated attacker with permission to create or modify NginxProxy resources can craft format strings containing NGINX configuration syntax—such as include directives, stream directives, or other configuration blocks—to break out of the intended logging context and inject arbitrary directives. The vector is network-accessible (AV:N), requires low attack complexity (AC:L), and demands authenticated access (PR:L) with no user interaction (UI:N). The impact is confined to confidentiality and integrity on the system under attack (S:U); availability is not directly affected.

Business impact

Organizations running NGINX Gateway Fabric in Kubernetes environments face a privilege-escalation path: an authenticated developer, operator, or insider with CRD write permissions can escalate to control NGINX configuration directly. This could lead to traffic interception, unauthorized access logging redirection, SSL/TLS certificate stripping, or further pivoting into backend services. In multi-tenant clusters where different teams manage their own ingress configurations, this becomes a cross-tenant boundary violation. Compliance frameworks requiring defense-in-depth and least-privilege access will flag this as a critical control-plane weakness.

Affected systems

The vulnerability affects NGINX Gateway Fabric in any configuration where NGINX Plus or NGINX Open Source serves as the data plane. Impact is limited to deployments where untrusted or insufficiently-privileged users can create or modify NginxProxy CRDs. Verify your NGINX Gateway Fabric version against vendor advisories for exact affected releases. Note that F5 does not evaluate software versions that have reached End of Technical Support.

Exploitability

Exploitation requires authentication (operator or developer role in Kubernetes) and explicit permission to create or modify NginxProxy resources. No special tools or complex techniques are needed beyond crafting a malformed access_log format string. The attack surface is internal to the control plane; external unauthenticated attackers cannot trigger this. However, in environments with overly-permissive role-based access control (RBAC) or shared service accounts, the barrier to exploitation is minimal. Once exploited, the attacker gains NGINX configuration control, which may enable further attacks on the data plane.

Remediation

Apply patches released by F5 for NGINX Gateway Fabric. Immediately audit and restrict RBAC permissions for NginxProxy CRD creation and modification to only trusted personnel. Implement network policies and admission controllers to validate or reject suspicious CRD configurations before they reach the control plane. In high-risk environments, disable or restrict the access_log format setting until patched, or pre-define format strings and prevent user modification.

Patch guidance

Consult the F5 security advisory and vendor documentation for specific patched versions of NGINX Gateway Fabric. Apply updates in a test environment first to confirm compatibility with your Kubernetes cluster and data-plane NGINX versions. Verify that the configuration generator properly escapes user-supplied strings in CRD fields after patching.

Detection guidance

Monitor Kubernetes audit logs for modifications to NginxProxy CRDs, particularly changes to the access_log format field. Look for entries containing NGINX directives (e.g., 'include', 'stream', 'server', 'location', braces, semicolons) in what should be a simple logging format string. Alert on CRD create/modify events from users or service accounts with unexpected permissions. Review NGINX configuration on the data plane for unexpected directives or includes that may have been injected. Implement webhook-based admission controllers to validate and reject CRD payloads containing suspicious patterns.

Why prioritize this

This vulnerability scores 8.1 (HIGH) due to the combination of high impact (confidentiality and integrity compromise), low attack complexity, and network accessibility. Although it requires authentication, the control-plane nature of the vulnerability and the ease of escalating to configuration control make it a priority for any organization running NGINX Gateway Fabric. The lack of mitigating factors (no CVSS CIA:C complexity, no isolation via separate privilege scope) elevates it above informational or moderate-severity issues.

Risk score, explained

CVSS 3.1 score of 8.1 reflects: Network-accessible attack vector (N), low attack complexity (L), and low privilege requirements (L—authenticated access only). The integrity and confidentiality impacts are High; availability is None. Scope is Unchanged, so the attacker is limited to the system under attack. The threat is immediate for organizations with inadequate RBAC policies and high-risk for those managing multi-tenant clusters where roles are delegated broadly.

Frequently asked questions