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CVE-2026-82456 – Authentication Bypass / Full Argo CD Takeover – argocd-mcp (argoproj-labs) 0.8.0

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Summary

CVE-2026-82456 is a critical authentication bypass vulnerability in argocd-mcp (the argoproj-labs Model Context Protocol server for Argo CD, mcp-for-argocd), affecting version 0.8.0. The MCP server binds its HTTP transport to all network interfaces and accepts MCP sessions without requiring any caller credentials whenever an ARGOCD_API_TOKEN is configured, allowing any network-reachable attacker to reuse the operator’s stored token to fully control the connected Argo CD instance. The flaw carries the maximum severity score of 10.0 (Critical).

Technical details

  • Root cause: The argocd-mcp HTTP transport listens on 0.0.0.0 (all interfaces) rather than restricting to localhost/loopback, and it does not enforce authentication or session-level authorization on incoming MCP client connections (CWE-1327: Binding to an Unrestricted IP Address).
  • Trigger condition: Exploitation requires that the operator has configured ARGOCD_API_TOKEN for the MCP server to interact with the Argo CD API — a standard deployment configuration.
  • Attack vector: Network (AV:N) — no privileges, no user interaction, and low attack complexity are required. Any attacker with network reachability to the exposed MCP HTTP port can open a session and issue commands as if they were the legitimate operator.
  • Impact: Because the MCP server holds and reuses the configured ARGOCD_API_TOKEN on behalf of any connecting client, an attacker can manipulate Argo CD resources, create new Applications, and trigger synchronization operations — effectively achieving full control over the Argo CD-managed GitOps pipeline and, by extension, the workloads it deploys.

Affected software

  • Product: argocd-mcp (argoproj-labs mcp-for-argocd)
  • Vulnerable version: 0.8.0 (and the 0.8.x line prior to the fix)
  • Fixed version: 0.9.0 and later

Severity

  • CVSS v3.1 Base Score: 10.0 (Critical)
  • Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
  • (A CVSS v4.0 score of 10.0 was also assigned: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H)

Mitigation and recommended actions

  • Immediate: Upgrade argocd-mcp to version 0.9.0 or later, which removes the unauthenticated, all-interfaces HTTP exposure.
  • If patching is not immediately possible:
    • Do not expose the argocd-mcp HTTP transport to untrusted networks; bind it to localhost or restrict access via firewall/network policy so only trusted local processes can reach it.
    • Avoid running argocd-mcp with ARGOCD_API_TOKEN configured on any instance reachable from shared or untrusted networks.
    • Rotate the ARGOCD_API_TOKEN used by any exposed MCP server instance, and review Argo CD audit logs for unauthorized Application creation or sync operations.
    • Place the MCP server behind an authenticating reverse proxy or VPN until upgraded.

References

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