ChatCLI: Improper validation in MCP OAuth login flow (CVE-2026-123271)

ChatCLI versions before 1.215.2 contain an improper validation vulnerability in the Model Context Protocol (MCP) OAuth login flow. The application uses server-supplied Protected Resource Metadata as a resource indicator without verifying that it matches the locally configured server URL. An attacker operating a malicious MCP server can cause the application to request an OAuth bearer token for a different, potentially sensitive resource hosted on the same authorization server and subsequently replay that token to impersonate the user against that resource.

Impact

Successful exploitation allows a malicious MCP server operator to obtain valid OAuth bearer tokens intended for different resources, leading to unauthorized access and user impersonation within the context of the shared authorization server.

Recommendation

• Upgrade ChatCLI to version 1.215.2 or later immediately to patch the validation logic flaw.
• Review OAuth authorization server logs for unusual token request patterns originating from MCP clients.
• In environments where upgrading is delayed, limit the use of MCP servers to trusted and verified sources.