AWS API MCP Server 1.5.1 Fixes Custom Security Policy Bypass
Tech GuruQuick Answer
Upgrade local AWS API MCP Server installations and forks to 1.5.1 or later. Test deny and elicitation rules for acronym-bearing operation names, review authorized API activity, and retain policy and version evidence.
Confirm Scope And Apply The Supported Remediation
What to do now: Record local server versions, custom policies, assistant integrations, AWS identities and owners. Check whether custom rules cover operation names with consecutive capital letters. Keep this MCP policy issue separate from AWS IAM authorization and from the unaffected remote offering. Upgrade to 1.5.1 or later and incorporate the fix into maintained forks. AWS states that there is no workaround other than upgrading. Verify the loaded server version after restart, test representative denied and confirmation-required operations with safe accounts, and retain policy tests and relevant CloudTrail records.
Last verified: 2026-11-10 UTC. Recheck the authoritative advisory and supported distribution channel before changing production.
Scope And Authority
| Product scope | Locally run AWS API MCP Server with custom security policies |
|---|---|
| Advisory | 2026-176-AWS / GHSA-4wq9-grf3-qg2p |
| CVE | CVE-2026-125271 |
| Authoritative release date | November 10, 2026 at 08:30 PST (16:30 UTC), from AWS bulletin 2026-176-AWS. |
| Authority revision date | No later revision is stated. |
| Affected versions | awslabs.aws-api-mcp-server >=0.2.13 and <1.5.1 with denyList or elicitList entries for operations containing consecutive capital letters. Exploitation requires interaction with the AI assistant. The remote service and READ_OPERATIONS_ONLY and REQUIRE_MUTATION_CONSENT settings are not affected. |
| Fixed version | awslabs.aws-api-mcp-server 1.5.1 or later |
| CVSS base score | 8.5 (project CVSS v4.0 base score) |
| CVSS severity | High |
| Exploitation status | AWS does not state malicious exploitation in the bulletin or project advisory.; no exploitation claim is inferred. |
What Changed
AWS corrected operation-name normalization that prevented some custom deny and elicitation rules from matching. A local MCP server could therefore allow AWS API actions that its operator intended to deny or require confirmation for.
What To Validate Now
- Inventory. Record local server versions, custom policies, assistant integrations, AWS identities and owners.
- Establish applicability. Check whether custom rules cover operation names with consecutive capital letters. Keep this MCP policy issue separate from AWS IAM authorization and from the unaffected remote offering.
- Remediate. Upgrade to 1.5.1 or later and incorporate the fix into maintained forks. AWS states that there is no workaround other than upgrading.
- Validate. Verify the loaded server version after restart, test representative denied and confirmation-required operations with safe accounts, and retain policy tests and relevant CloudTrail records.
- Retain evidence. Preserve asset and owner identifiers, the applicability decision, before-and-after versions, change approval, installation output, validation results, and any exception or rollback record.
Operational Cautions
Do not test destructive cloud actions against production resources. Existing MCP guard settings do not establish that custom rules are effective; preserve audit records before investigating unexpected actions.
Evidence To Retain
- Exact product, release stream, package or application version, enabled feature, environment, and accountable owner.
- UTC timestamps, authority revision, approved change record, installer or package-manager output, and resulting version.
- Relevant logs and monitoring evidence, test results, exceptions, compensating controls, and rollback decisions.
Related TechGeeks Resources
Authoritative References
Correction policy: If the authority changes affected versions, fixed versions, severity, exploitation information, mitigations, or required action, TechGeeks will update this notice and its verification date.
