CVE-2026-16584 is a high-severity (CVSS 7) CWE-455 vulnerability in awslabs-aws-api-mcp-server. A fix is available for awslabs-aws-api-mcp-server — see the affected versions and patch details below.
AWS API MCP Server Security Policy Bypass via Startup Initialization Failure
Exploitation Status
No confirmed exploitation observed yet
- A successful exploit gives an attacker total control of the affected component, not partial access.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-16584.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2026-16584 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 394,803 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
awslabs-aws-api-mcp-serverReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.
Description
Summary
The AWS API MCP Server is an open source Model Context Protocol (MCP) server that enables AI assistants to interact with AWS services and resources through AWS CLI commands. It provides programmatic access to manage your AWS infrastructure while maintaining proper security controls. It includes an optional, user-configured security policy that can deny or gate specific AWS operations. An issue exists where, if the data used to enforce this policy fails to initialize at server startup, the per-request policy check is silently skipped for the lifetime of the process.
Impact
On startup, the server loads data used to enforce the configured security policy. If that load fails, the server continues running without the enforcement data in place. In the default configuration, the per-request security check is then bypassed for the lifetime of the process: configured deny and gate rules are not consulted, and AWS API operations the policy was intended to restrict execute without enforcement. The scope is limited to the security-policy gate; IAM permissions on the configured credentials remain in effect and continue to bound what the server can do.
Impacted versions: >= 0.2.13 AND < 1.3.47
Patches
This issue has been addressed in awslabs.aws-api-mcp-server version 1.3.47. AWS recommends upgrading to the latest version and ensuring any forked or derivative code is patched to incorporate the new fixes.
Workarounds
Any one of the following prevents the bypass until you can upgrade:
- Use least-privilege IAM credentials (for example, a ReadOnlyAccess role) scoped to the task. IAM remains the primary access control and is enforced regardless of this issue.
- If the server started during degraded connectivity, restart it once connectivity is restored so the policy enforcement data loads successfully.
Contact
If you have any questions or comments about this advisory, AWS asks that you contact AWS Security via the reporting page or directly via email to [email protected]. Please do not create a public GitHub issue.
Acknowledgement
We would like to thank Lav Kumar Vishwakarma (independent security researcher) for collaborating on this issue through the coordinated vulnerability disclosure process.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | awslabs-aws-api-mcp-server | ≥ 0.2.13&&< 1.3.47 | 1.3.47pip install --upgrade 'awslabs-aws-api-mcp-server==1.3.47' |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for awslabs-aws-api-mcp-server, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update awslabs-aws-api-mcp-server to 1.3.47 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-16584 is resolved across your whole dependency graph.
Workarounds
Put an independent control in front of the weakness: restrict the affected endpoint or interface to trusted networks, require an additional authentication factor or proxy-level check, and invalidate existing sessions and credentials in case the flaw has already been used.
Frequently Asked Questions
Is CVE-2026-16584 in your dependencies?
Find it across PyPI, including transitive dependencies.