CVE-2025-59538 is a vulnerability in Argo CD, a popular GitOps continuous delivery tool for Kubernetes, affecting multiple versions from 2.9.0-rc1 up to 2.14.19 and certain 3.x release candidates and minor versions. The flaw exists in the /api/webhook endpoint handling Azure DevOps push events. Specifically, when the configuration parameters webhook.azuredevops.username and webhook.azuredevops.password are unset, the server processes incoming webhook payloads without verifying the length of the resource.refUpdates JSON array. If this array is empty, the code attempts to access the first element (index 0) without bounds checking, causing an index-out-of-range panic that crashes the argocd-server process. This results in a denial of service as the server becomes unavailable until restarted. The vulnerability can be triggered by an unauthenticated attacker sending a single HTTP POST request with a crafted payload containing an empty resource.refUpdates array. No authentication or user interaction is required, and the attack surface is exposed over the network. The issue is tracked under CWE-248 (Uncaught Exception) and CWE-703 (Improper Check or Handling of Exceptional Conditions). The vulnerability has a CVSS v3.1 score of 7.5 (high severity) due to its network attack vector, lack of required privileges, and impact on availability. No known exploits are reported in the wild as of publication. The vulnerability is resolved in Argo CD versions 2.14.20, 3.2.0-rc2, 3.1.8, and 3.0.19 by adding proper input validation and error handling to prevent the panic and crash.

For European organizations, this vulnerability poses a significant risk of denial of service in Kubernetes environments using Argo CD for continuous delivery. As Argo CD is widely adopted for GitOps workflows, a successful exploit can disrupt deployment pipelines, delay software delivery, and impact business continuity. The unauthenticated nature of the attack means that any external or internal actor with network access to the argocd-server endpoint can trigger the crash, potentially leading to repeated service outages. This can affect critical infrastructure, cloud-native applications, and DevOps automation processes. Organizations relying on Azure DevOps integration with Argo CD are particularly vulnerable if webhook credentials are not configured. The disruption could also increase operational costs due to incident response and recovery efforts. While no data confidentiality or integrity impact is reported, the availability impact alone can have cascading effects on dependent services and SLAs.

European organizations should immediately upgrade affected Argo CD instances to the fixed versions: 2.14.20, 3.2.0-rc2, 3.1.8, or 3.0.19, depending on their current version. If immediate upgrade is not feasible, ensure that webhook.azuredevops.username and webhook.azuredevops.password are properly set in the configuration to prevent the vulnerable code path from being triggered. Implement network-level access controls to restrict inbound traffic to the /api/webhook endpoint, limiting exposure to trusted sources only. Monitor argocd-server logs for unexpected crashes or webhook payload anomalies, and consider deploying runtime protection or crash recovery mechanisms to minimize downtime. Conduct security reviews of webhook integrations and validate incoming payloads at the ingress level to detect malformed or suspicious requests. Finally, incorporate this vulnerability into incident response and patch management workflows to ensure timely remediation.