CVE-2026-16584 is a high-severity (CVSS 7) CWE-455 vulnerability in awslabs-aws-api-mcp-server. O3 Security confirms whether CVE-2026-16584 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
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
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2026-16584 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 369,023 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
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 | 1.3.47 |
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. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
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
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2026-16584 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2026-16584. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-16584 in your dependencies?
O3 detects CVE-2026-16584 across PyPI dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.