CVE-2026-77180: 
NGINX Ingress Controller (NGINX Inc) vulnerability analysis and mitigation

CVE-2026-77180 is a configuration injection vulnerability in F5's NGINX Ingress Controller affecting versions 5.0.0 through 5.5.x (fixed in 5.6.0) and the 2026-lts-r1 through 2026-lts-r4 releases (fixed in 2026-lts-r5). The vulnerability exists in the controller's configuration generator, where multiple user-controllable Ingress annotation fields are written into the generated NGINX configuration without sanitization, enabling authenticated attackers to inject arbitrary NGINX directives. It was published on September 2, 2026, with a patch made available the same day. The vulnerability carries a CVSS v4.0 base score of 8.7 (High) and a CVSS v3.1 base score of 8.3 (High) (GitHub Advisory, F5 Advisory).

The root cause is classified as CWE-76 (Improper Neutralization of Equivalent Special Elements): the configuration generator fails to sanitize user-supplied values in Ingress annotations before embedding them into the NGINX configuration file. An authenticated attacker with Kubernetes API write access to Ingress resources can craft annotation values containing NGINX configuration directives — such as newline-delimited blocks or equivalent special characters — that are interpreted by NGINX when the configuration is applied. Exploitation requires low privileges (write access to Ingress annotations via the Kubernetes API) and no user interaction, and is network-accessible with low attack complexity. This is strictly a control plane issue; the data plane is not directly exposed (GitHub Advisory).

A successful exploit allows an authenticated attacker to inject arbitrary NGINX configuration directives into the controller's generated configuration, potentially enabling creation or deletion of files on the controller host, disabling services, or manipulating routing and proxy behavior. Confidentiality and integrity impacts are rated High, as an attacker could redirect traffic, expose sensitive configuration data, or alter service behavior; availability impact is rated Low. The vulnerability is scoped to the control plane only — there is no direct data plane exposure, limiting lateral movement to the Kubernetes control plane environment (GitHub Advisory, F5 Advisory).

As of the disclosure date, there is no public proof-of-concept exploit and no evidence of in-the-wild exploitation (GitHub Advisory). The EPSS score is approximately 0.307% (23rd percentile), indicating a low near-term exploitation probability. The vulnerability is not listed in the CISA Known Exploited Vulnerabilities (KEV) catalog. NVD's SSVC assessment classifies exploitation as "none" and the vulnerability as non-automatable, reflecting the requirement for authenticated access with specific Kubernetes RBAC permissions.

1. Reconnaissance: Identify a target Kubernetes cluster running NGINX Ingress Controller versions 5.0.0–5.5.x or 2026-lts-r1 through 2026-lts-r4 using cluster version enumeration or public exposure scanning.
2. Obtain credentials: Acquire Kubernetes API credentials with write access to Ingress resources (e.g., through a compromised service account, misconfigured RBAC, or a legitimate low-privilege user account).
3. Craft malicious annotation: Construct an Ingress resource or modify an existing one with a crafted annotation value containing injected NGINX configuration directives. For example, embed newline characters or equivalent special elements in annotation fields (such as nginx.ingress.kubernetes.io/configuration-snippet) to introduce arbitrary server or location block directives.
4. Apply the Ingress resource: Submit the crafted Ingress manifest via kubectl apply or the Kubernetes API, causing the NGINX Ingress Controller to regenerate its configuration incorporating the injected directives.
5. Achieve objective: The injected NGINX directives take effect upon configuration reload, potentially enabling traffic interception, file creation/deletion on the controller, or service disruption (GitHub Advisory, F5 Advisory).

• Kubernetes API Logs: Unexpected creation or modification of Ingress resources by low-privilege service accounts or users; audit log entries showing CREATE or UPDATE operations on Ingress objects with unusual annotation values containing newline characters, semicolons, or NGINX directive keywords.
• NGINX Configuration: Presence of unexpected directives in the generated NGINX configuration file (e.g., nginx.conf) such as unauthorized server, location, access_log, or include blocks not corresponding to legitimate Ingress definitions.
• File System: Unexpected files created or deleted in directories accessible to the NGINX Ingress Controller process; new or modified configuration snippets in the controller's working directory.
• Process/Service: Unexpected NGINX configuration reload events (nginx -s reload) triggered outside of normal deployment cycles; NGINX error logs indicating configuration parse errors or unusual directive processing.

F5 has released patched versions: NGINX Ingress Controller 5.6.0 and 2026-lts-r5; upgrading to these versions is the primary recommended remediation (GitHub Advisory, F5 Advisory). As a workaround prior to patching, restrict write access to Ingress resources and their annotations using Kubernetes RBAC policies, limiting which users and service accounts can create or modify Ingress objects. Additionally, monitor Kubernetes audit logs for suspicious Ingress annotation modifications and consider disabling annotation-based configuration snippets if not required by your deployment. Note that versions that have reached End of Technical Support (EoTS) will not receive patches.