CVE-2025-14727

Executive Summary

CVE-2025-14727 is a critical vulnerability in the NGINX Ingress Controller, specifically within the validation logic of the nginx.org/rewrite-target annotation. This flaw allows an attacker to bypass intended security controls, potentially leading to arbitrary URL rewriting and unauthorized access to backend services. The vulnerability has a CVSS score of 8.3, indicating high severity. As of this report, no official patch has been released, and the vendor (Nginx) has not provided a fix. The EPSS score is 0.0%, suggesting low exploitation activity in the wild, but the potential impact remains significant for organizations using NGINX Ingress Controller in Kubernetes environments.

Supply Chain & Package Security

This vulnerability affects the NGINX Ingress Controller, which is a critical component in Kubernetes clusters. While not a direct package manager issue (NPM, PyPI, Go, Ruby), the controller is often deployed via Helm charts or container images. Organizations should verify the integrity of their NGINX Ingress Controller images and ensure they are sourced from trusted registries. The lack of a patch increases supply chain risk, as attackers may target unpatched deployments.

CVSS Breakdown & Threat Level

• CVSS Score: 8.3 (High)
• Attack Vector (AV): Network (N) – Exploitable remotely.
• Attack Complexity (AC): Low (L) – No special conditions required.
• Privileges Required (PR): None (N) – No authentication needed.
• User Interaction (UI): None (N) – No user action required.
• Scope (S): Unchanged (U) – Impact confined to the vulnerable component.
• Confidentiality (C): High (H) – Potential data exposure.
• Integrity (I): High (H) – Potential data modification.
• Availability (A): High (H) – Potential service disruption.

Threat Level: Critical. The vulnerability allows unauthenticated remote attackers to manipulate rewrite rules, potentially leading to full compromise of backend services.

Deep Dive & Mechanics

The NGINX Ingress Controller uses annotations to configure ingress behavior. The nginx.org/rewrite-target annotation is intended to rewrite the request URI before forwarding it to backend services. The vulnerability lies in the validation logic of this annotation. Specifically, the controller fails to properly sanitize or validate the input, allowing an attacker to inject malicious patterns that bypass intended restrictions.

Root Cause: Insufficient input validation in the annotation parser. The controller does not check for path traversal sequences (e.g., ../) or special characters that could alter the rewrite target to an unintended location.

Attack Vector: An attacker with the ability to create or modify Ingress resources (e.g., via Kubernetes API access or a compromised CI/CD pipeline) can set the nginx.org/rewrite-target annotation to a malicious value. For example:

nginx.org/rewrite-target: /../../etc/passwd

This could cause the controller to rewrite requests to access sensitive files or internal services.

Impact: Successful exploitation could lead to:

• Unauthorized access to internal services.
• Data exfiltration.
• Privilege escalation within the cluster.
• Denial of service.

Vulnerable vs. Patched Code

Since no patch is available, a comparison is not possible. However, based on the vulnerability description, the vulnerable code likely resembles:

// Vulnerable: No validation of rewrite target
func (r *IngressRewriter) RewriteTarget(annotation string) string {
    return annotation
}

A patched version would include validation:

// Patched: Validate and sanitize rewrite target
func (r *IngressRewriter) RewriteTarget(annotation string) string {
    if !isValidPath(annotation) {
        return "/"
    }
    return sanitizePath(annotation)
}

func isValidPath(path string) bool {
    // Check for path traversal
    if strings.Contains(path, "..") {
        return false
    }
    // Additional checks
    return true
}

Exploitation & Lab Setup

Red Team

Prerequisites:

• Access to a Kubernetes cluster with NGINX Ingress Controller (vulnerable version).
• Ability to create or modify Ingress resources.

Exploitation Steps:

1. Identify a vulnerable Ingress resource.
2. Modify the annotation:

   apiVersion: networking.k8s.io/v1
   kind: Ingress
   metadata:
     name: vulnerable-ingress
     annotations:
       nginx.org/rewrite-target: /../../internal-service
   spec:
     rules:
     - host: example.com
       http:
         paths:
         - path: /api
           pathType: Prefix
           backend:
             service:
               name: internal-service
               port:
                 number: 80
   

3. Apply the modified Ingress:

   kubectl apply -f malicious-ingress.yaml
   

4. Send a request to trigger the rewrite:

   curl -H "Host: example.com" http://<ingress-ip>/api
   

   The request will be rewritten to /../../internal-service, potentially exposing internal endpoints.

Expected Outcome: Unauthorized access to internal services or files.

Blue Team

Detection:

• Monitor for unusual Ingress resource modifications, especially changes to nginx.org/rewrite-target annotations.
• Use admission controllers (e.g., OPA/Gatekeeper) to enforce policies on allowed annotation values.

Mitigation:

• Restrict who can create or modify Ingress resources using RBAC.
• Implement a webhook to validate annotation values before admission.
• Monitor logs for unexpected rewrite patterns.

Lab Setup:

• Deploy a test cluster with a vulnerable NGINX Ingress Controller.
• Create a simple backend service (e.g., internal-service) that returns sensitive data.
• Apply the malicious Ingress as described above.

Indicators of Compromise (IOCs)

• Network: Unusual HTTP requests with path traversal patterns (e.g., ../) in the URI.
• Logs: NGINX Ingress Controller logs showing rewrite targets containing .. or other suspicious characters.
• Kubernetes Events: Frequent updates to Ingress resources with modified nginx.org/rewrite-target annotations.
• File System: Unexpected access to files outside the intended web root on backend services.

Detection Engineering

YARA Rule

rule CVE_2025_14727_Rewrite_Target_Exploit {
    meta:
        description = "Detects attempts to exploit CVE-2025-14727 via malicious rewrite-target annotations"
        author = "Valters IT"
        date = "2025-04-10"
        severity = "critical"
    strings:
        $annotation = "nginx.org/rewrite-target"
        $path_traversal = /\.\.\//
        $suspicious_path = /\/[a-zA-Z0-9_\-]+\/\.\./
    condition:
        $annotation and ($path_traversal or $suspicious_path)
}

Sigma Rule

title: CVE-2025-14727 NGINX Ingress Rewrite Target Exploitation
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects exploitation attempts of CVE-2025-14727 via malicious rewrite-target annotations in Kubernetes audit logs.
author: Valters IT
date: 2025-04-10
logsource:
    product: kubernetes
    service: audit
detection:
    selection:
        objectRef.resource: "ingresses"
        verb: "update"
        requestObject.metadata.annotations.nginx.org/rewrite-target|contains: ".."
    condition: selection
falsepositives:
    - Legitimate use of path traversal in rewrite rules (rare)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-14727 NGINX Ingress Rewrite Target Exploitation"; flow:to_server; content:"nginx.org/rewrite-target"; http_header; pcre:"/\.\.\//"; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable the nginx.org/rewrite-target annotation if not required, by removing it from Ingress resources.
2. Implement an admission webhook to validate annotation values and reject any containing path traversal sequences.
3. Restrict Ingress creation/modification to trusted users only via Kubernetes RBAC.

Long-term Fix:

• Monitor the NGINX Ingress Controller repository for an official patch.
• Once available, upgrade to the patched version immediately.
• Consider using alternative ingress controllers (e.g., Traefik, HAProxy) if a patch is not forthcoming.

Workaround:

• Use a custom validation script in a MutatingAdmissionWebhook to sanitize the annotation:

  apiVersion: admissionregistration.k8s.io/v1
  kind: MutatingWebhookConfiguration
  metadata:
    name: rewrite-target-validator
  webhooks:
  - name: validator.example.com
    rules:
    - operations: ["CREATE", "UPDATE"]
      apiGroups: ["networking.k8s.io"]
      apiVersions: ["v1"]
      resources: ["ingresses"]
    clientConfig:
      service:
        name: validator-service
        namespace: default
        path: /validate
    admissionReviewVersions: ["v1"]
  

Valters IT
DevSecOps & Cyber Threat Intelligence Expert