CVE-2026-16584: CWE-455 Non-exit on failed initialization in AWS aws-api-mcp-server
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.
AI Analysis
Technical Summary
The AWS API MCP Server (awslabs.aws-api-mcp-server) loads user-configured security policy data on startup to enforce restrictions on AWS CLI commands executed by AI assistants. CVE-2026-16584 arises when this initialization fails but the server does not exit; instead, it continues running with the per-request policy checks disabled for the lifetime of the process. If fail-closed mode is not enabled, this allows an actor to bypass the configured policy restrictions and execute AWS API operations that should be denied or gated. The vulnerability affects versions >=0.2.13 and <1.3.47. IAM permissions on credentials remain enforced, but the security policy bypass increases risk. AWS provides a security bulletin with remediation details and manages patching for this cloud service.
Potential Impact
If the security policy initialization fails and fail-closed mode is not enabled, the aws-api-mcp-server will skip policy enforcement, allowing AWS API operations normally denied or gated by the policy to execute. This could lead to unauthorized actions within the scope of the IAM permissions of the configured credentials. The vulnerability impacts confidentiality, integrity, and availability as indicated by the CVSS vector (C:H/I:H/A:H). However, IAM permissions remain intact and are not bypassed by this vulnerability.
Mitigation Recommendations
AWS manages remediation for this cloud-hosted service. Users should refer to the official AWS Security Bulletin (https://aws.amazon.com/security/security-bulletins/2026-063-aws/) for the most current guidance. It is recommended to enable fail-closed mode in the security policy configuration to ensure the server does not continue running without enforcement if initialization fails. Applying the latest updates or patches provided by AWS for the aws-api-mcp-server is advised.
CVE-2026-16584: CWE-455 Non-exit on failed initialization in AWS aws-api-mcp-server
Description
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.
CVSS v3.1
Score 7.0high
Affected software
pkg:pypi/awslabs-aws-api-mcp-serverRun on your own infrastructure? Check whether these packages are installed with threat-finder — our free open-source scanner.
Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
The AWS API MCP Server (awslabs.aws-api-mcp-server) loads user-configured security policy data on startup to enforce restrictions on AWS CLI commands executed by AI assistants. CVE-2026-16584 arises when this initialization fails but the server does not exit; instead, it continues running with the per-request policy checks disabled for the lifetime of the process. If fail-closed mode is not enabled, this allows an actor to bypass the configured policy restrictions and execute AWS API operations that should be denied or gated. The vulnerability affects versions >=0.2.13 and <1.3.47. IAM permissions on credentials remain enforced, but the security policy bypass increases risk. AWS provides a security bulletin with remediation details and manages patching for this cloud service.
Potential Impact
If the security policy initialization fails and fail-closed mode is not enabled, the aws-api-mcp-server will skip policy enforcement, allowing AWS API operations normally denied or gated by the policy to execute. This could lead to unauthorized actions within the scope of the IAM permissions of the configured credentials. The vulnerability impacts confidentiality, integrity, and availability as indicated by the CVSS vector (C:H/I:H/A:H). However, IAM permissions remain intact and are not bypassed by this vulnerability.
Mitigation Recommendations
AWS manages remediation for this cloud-hosted service. Users should refer to the official AWS Security Bulletin (https://aws.amazon.com/security/security-bulletins/2026-063-aws/) for the most current guidance. It is recommended to enable fail-closed mode in the security policy configuration to ensure the server does not continue running without enforcement if initialization fails. Applying the latest updates or patches provided by AWS for the aws-api-mcp-server is advised.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- AMZN
- Date Reserved
- 2026-07-22T13:43:35.240Z
- Cvss Version
- 3.1
- State
- PUBLISHED
- Remediation Level
- null
- Is Cloud Service
- true
- Vendor Advisory Urls
- [{"url":"https://aws.amazon.com/security/security-bulletins/2026-063-aws/","vendor":"AWS"}]
Threat ID: 6a623fe59c2644c7f85af557
Added to database: 07/23/2026, 16:23:01 UTC
Last enriched: 08/15/2026, 18:31:33 UTC
Last updated: 09/06/2026, 10:52:07 UTC
Views: 210
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