Unpatched Argo CD Repo-Server Flaw Could Let Attackers Take Over Kubernetes Clusters

A significant security vulnerability has been identified within Argo CD, a widely adopted tool for managing software deployments on Kubernetes. The flaw, residing in the `repo-server` component, allows an unauthenticated attacker to execute arbitrary code, posing a severe risk of full Kubernetes cluster compromise. Security research firm Synacktiv initially reported this vulnerability to Argo CD's maintainers in January 2025. Despite the lapse of approximately eighteen months, the issue remains unpatched, leading Synacktiv to make a public disclosure to alert users and administrators. The core of the problem lies in the `repo-server`'s internal gRPC service, which operates without authentication. This absence of authentication means that any attacker who can reach this internal network port can send specially crafted requests to execute commands. Synacktiv demonstrated this attack against Argo CD v2.13.3, confirming the exploitability. While a comprehensive list of all affected versions was not released, the issue is present in versions utilizing the vulnerable `repo-server` component. The attack vector involves abusing `kustomize`, a standard tool used by Argo CD to transform Git repository files into Kubernetes manifests. Specifically, the `--helm-command` option within `kustomize` can be manipulated to point to a malicious `helm` binary. This allows an attacker, even after compromising a single pod within the cluster, to reach the `repo-server` and trigger the vulnerability. Once code execution is achieved on the `repo-server`, attackers can escalate their privileges. Synacktiv's proof-of-concept involved reading the cluster's Redis password from an environment variable, connecting to Argo CD's Redis cache, and then poisoning the stored deployment data. This manipulation could result in Argo CD automatically deploying attacker-supplied workloads during its next synchronization cycle. This scenario also highlights a potential re-exploitation of CVE-2024-31989, a previous flaw where an unauthenticated Redis instance allowed for deployment cache poisoning. This incident is not an isolated one for Argo CD. Previous vulnerabilities, such as CVE-2025-55190 (September 2025) which allowed API tokens with basic read access to retrieve Git repository credentials, and CVE-2026-42880 (May 2026) enabling read-only users to access plaintext Kubernetes secrets, indicate a recurring pattern of internal exposure. These vulnerabilities underscore the critical importance of robust security practices and network segmentation when deploying and managing Argo CD in production environments.