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

unknownCVE-2026-16584

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 < 1.3.47 Please refer to the article below for the most up-to-date and complete information related to this AWS Security Bulletin.

CSIRTS triage

vendor: AWS product: AWS API MCP Server Authentication bypass

What: A security policy bypass vulnerability exists due to a failure in server startup initialization.
Who is affected: Users of the AWS API MCP Server with configured security policies.
Urgency: Remediation is important as it could allow unauthorized AWS operations, but exploitation is not confirmed.
Action: Users should review and update their security policies and monitor server startup processes.

AI-assisted analysis generated from the source advisory — verify against the original.

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Details

Source: AWS Security Bulletins (INTL · vendor-psirt · site)
Severity: unknown
Published: 2026-08-20
Exploitation: Not in CISA KEV at last sync

Original advisory: https://aws.amazon.com/security/security-bulletins/rss/2026-063-aws/

Exploitation outlook

EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.

Low exploitation riskCVE-2026-165840.16% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 5% of all EPSS-scored CVEs.

Referenced CVEs

CVE	CSIRTS overview	External
CVE-2026-16584	coverage & exploitation status	NVD · CVE.org

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