CVE-2026-29954: KubePlus SSRF Vulnerability

CVE-2026-29954 Overview

CVE-2026-29954 is a Server-Side Request Forgery (SSRF) and Command Injection vulnerability affecting KubePlus 4.1.4. The vulnerability exists in the mutating webhook and kubeconfiggenerator components when processing the chartURL field of ResourceComposition resources. While the field is URL-encoded, the implementation fails to validate the target address. More critically, when kubeconfiggenerator uses wget to download charts, the chartURL is directly concatenated into the command line, enabling attackers to inject wget's --header option to achieve arbitrary HTTP header injection.

Critical Impact

Attackers with high privileges can exploit this vulnerability to perform SSRF attacks against internal services and inject arbitrary HTTP headers, potentially leading to sensitive data exfiltration or further attack chains within Kubernetes clusters.

Affected Products

• KubePlus 4.1.4

Discovery Timeline

• 2026-03-30 - CVE-2026-29954 published to NVD
• 2026-04-01 - Last updated in NVD database

Technical Details for CVE-2026-29954

Vulnerability Analysis

This vulnerability combines two distinct security flaws classified under CWE-88 (Improper Neutralization of Argument Delimiters in a Command). The first issue is a Server-Side Request Forgery (SSRF) flaw where the chartURL field in ResourceComposition resources is not properly validated against internal or restricted network addresses. The second, more severe issue, involves command injection through argument manipulation.

When the kubeconfiggenerator component processes chart downloads, it constructs a shell command using wget and directly concatenates the user-supplied chartURL value. This lack of proper input sanitization allows attackers to break out of the intended URL parameter and inject additional wget arguments such as --header, enabling arbitrary HTTP header injection in outgoing requests.

Root Cause

The root cause is improper input validation and unsafe command construction in the kubeconfiggenerator component. The chartURL field undergoes URL encoding but lacks validation to prevent SSRF attacks against internal addresses. Furthermore, the direct string concatenation of user input into shell commands without proper escaping or argument separation creates a command injection vector. The application fails to use safe command execution patterns such as argument arrays or parameterized command execution.

Attack Vector

The attack requires network access and high privileges within the Kubernetes environment. An attacker with sufficient permissions to create or modify ResourceComposition resources can craft a malicious chartURL value containing injected wget arguments. By including the --header flag in the URL, attackers can add arbitrary HTTP headers to outgoing requests made by the kubeconfiggenerator component.

This can be leveraged to:

• Perform SSRF attacks against internal services within the Kubernetes cluster
• Exfiltrate sensitive data through controlled external endpoints via custom headers
• Bypass authentication mechanisms that rely on HTTP headers
• Interact with cloud metadata services (e.g., AWS IMDSv1)

The vulnerability achieves a changed scope, meaning the impact extends beyond the vulnerable component itself, potentially affecting other services in the infrastructure.

Detection Methods for CVE-2026-29954

Indicators of Compromise

• Unusual outbound HTTP requests from kubeconfiggenerator pods to internal IP addresses or cloud metadata endpoints
• ResourceComposition resources containing suspicious chartURL values with embedded --header or other wget flags
• Kubernetes audit logs showing creation or modification of ResourceComposition resources with malformed URLs
• Network traffic from KubePlus components containing unexpected HTTP headers

Detection Strategies

• Monitor Kubernetes audit logs for ResourceComposition resource creation/modification events with unusual chartURL patterns
• Implement network segmentation and monitor for SSRF attempts targeting internal services (169.254.169.254, 10.x.x.x ranges)
• Deploy runtime security tools to detect command injection patterns in pod processes
• Create alerts for wget processes spawned by kubeconfiggenerator with unexpected command-line arguments

Monitoring Recommendations

• Enable verbose logging on KubePlus components to capture full request details
• Implement egress filtering and monitoring for unexpected outbound connections from KubePlus pods
• Deploy Kubernetes admission controllers to validate ResourceComposition manifests before acceptance
• Utilize SentinelOne Singularity for Cloud Workload Security to monitor container behavior and detect anomalous process execution

How to Mitigate CVE-2026-29954

Immediate Actions Required

• Audit all existing ResourceComposition resources for suspicious chartURL values
• Implement network policies to restrict egress from KubePlus components to only required chart repositories
• Deploy admission controllers to validate and sanitize chartURL fields before resource creation
• Consider temporarily disabling the affected components if they are not critical to operations

Patch Information

Review the official KubePlus repository and security advisories for updated versions that address this vulnerability. Technical details and proof-of-concept information are available through the GitHub PoC Gist and the CVE-2026-29954 README.

Workarounds

• Implement strict URL validation at the Kubernetes admission controller level to reject chartURL values containing shell metacharacters or unexpected arguments
• Deploy network policies limiting kubeconfiggenerator egress to approved chart repository domains only
• Use OPA Gatekeeper or Kyverno policies to enforce allowed URL patterns for ResourceComposition resources
• Temporarily restrict RBAC permissions to prevent untrusted users from creating or modifying ResourceComposition resources

# Example Kubernetes NetworkPolicy to restrict egress
apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: restrict-kubeplus-egress
  namespace: kubeplus
spec:
  podSelector:
    matchLabels:
      app: kubeconfiggenerator
  policyTypes:
  - Egress
  egress:
  - to:
    - ipBlock:
        cidr: 0.0.0.0/0
        except:
        - 10.0.0.0/8
        - 172.16.0.0/12
        - 192.168.0.0/16
        - 169.254.169.254/32
    ports:
    - protocol: TCP
      port: 443