argocd-mcp 0.8.0 contains an authentication bypass flaw that allows an unauthenticated attacker to open MCP sessions without credentials when the environment variable ARGOCD_API_TOKEN is set. The vulnerability is a false negative string comparison (CWE-1327). As a result an attacker who can reach the exposed HTTP interface can create applications, trigger syncs, and modify Argo CD resources using the operator’s stored token. The impact is therefore unauthorized, privilege‑escalating access to the entire Argo CD management plane.

The flaw is present in the version 0.8.0 of argoproj‑labs:argocd‑mcp. No other versions are listed as affected.

The CVSS score of 10 indicates the highest risk severity. Because the service binds to all network interfaces, any host that can reach the listener can exploit the flaw without prior authentication or elevated privileges. The EPSS score is 1%, but the lack of an official KEV listing does not diminish the potential impact. The likely attack vector is network access to the public or internal interface where the MCP service is listening. Given the complete loss of authentication, exploitation is highly feasible and would allow attackers to create applications, trigger syncs, and modify Argo CD resources.