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

A critical, unpatched vulnerability in Argo CD's repo-server component poses a severe risk of Kubernetes cluster compromise, according to security researchers at Synacktiv. The flaw enables unauthenticated attackers to execute arbitrary code on the repo-server, potentially leading to a complete takeover of the Kubernetes cluster. Synacktiv initially reported this vulnerability to Argo CD's maintainers in January 2025. However, after approximately eighteen months without a fix, the firm decided to publicly disclose the details to alert users to the potential danger. The vulnerability resides in the repo-server's internal gRPC service, which, critically, lacks authentication. This absence of authentication means that any attacker capable of reaching this internal network port can send specially crafted requests to execute commands. The attack methodology demonstrated by Synacktiv involves abusing the `kustomize` tool, which Argo CD utilizes to transform Git repository files into Kubernetes manifests. Specifically, the `--helm-command` option within `kustomize` can be exploited. If an attacker gains control of a single pod within the cluster, they can leverage this access to reach the vulnerable repo-server. Once code execution is achieved on the repo-server, the attackers can further escalate their privileges. Synacktiv showed that this access could be used to extract the cluster's Redis password from environment variables. With the Redis password, they could then connect to Argo CD's Redis cache and inject malicious deployment data. This poisoned data would then be deployed by Argo CD during its next automatic synchronization cycle, allowing the attacker to deploy their own workloads onto the cluster. This particular step also revives a previous vulnerability, CVE-2024-31989, discovered by Cycode in 2024, where an unauthenticated Redis instance could be used to poison the deployment cache. This isn't the first time Argo CD has faced internal security exposures. Previous vulnerabilities include CVE-2025-55190 in September 2025, which allowed API tokens with basic read access to retrieve Git repository credentials, and CVE-2026-42880 in May 2026, which permitted read-only users to access plaintext Kubernetes secrets. The recurring nature of these vulnerabilities underscores a pattern where Argo CD, despite being a central tool for Kubernetes deployments, concentrates significant cluster access and repository secrets, and its internal components have repeatedly exposed these sensitive assets through unauthenticated or low-privilege access. Effective network segmentation and diligent application of patches are crucial for mitigating such risks.