CVE-2026-16584 - AWS API MCP Server Security Policy Bypass via Startup Failure

Bulletin ID: 2026-063-AWS Scope: AWS Content Type: Important (requires attention) Publication Date: 07/23/2026 08:30 AM PDT Description: The AWS API MCP Server (awslabs.aws-api-mcp-server) is an open-source MCP server that lets AI assistants execute AWS CLI commands against a user's AWS account. It includes an optional, user-configured security policy that can deny or gate specific AWS operations. We identified CVE-2026-16584. On startup, the server loads the data used to enforce this security policy. If that initialization fails, the server continues running with the per-request policy check skipped for the lifetime of the process. When a security policy is configured without the fail-closed modes enabled, an actor could then cause AWS API operations that the policy was configured to deny or gate to execute without enforcement. IAM permissions on the configured credentials remain in effect and are unaffected. Impacted versions: >= 0.2.13 AND
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