AmazonAnalysisAWS patches security policy bypass in AWS API MCP Server allowing unauthorized tool calls
What happened.Amazon Web Services published security bulletin 2026-176-AWS detailing a policy bypass vulnerability in its open-source Model Context Protocol server.
Why it matters.Model Context Protocol servers give artificial intelligence assistants programmatic access to cloud APIs. When case normalization errors let API calls bypass deny lists, autonomous agents execute destructive actions without required approvals. Cloud engineers must upgrade AWS API MCP servers to version 1.5.1 immediately.
The technical specifications:
- Vulnerability mechanics: Tracked as CVE-2026-125271 and GHSA-4wq9-grf3-qg2p, the defect affects security policy enforcement in awslabs.aws-api-mcp-server versions 0.2.13 through 1.5.0.
- Normalization failure: The server normalizes operation names incorrectly when evaluating API calls containing consecutive capital letters against configured policies.
- Policy evasion: Affected operations fail to match operator denyList rules, allowing artificial intelligence assistants to execute prohibited API actions without approval.
- Remediation release: AWS resolved the issue in version 1.5.1 by correcting operation name casing conversion before policy evaluation.
- Operational guidance: AWS confirmed no workaround exists, advising all teams running containerized or local MCP servers to upgrade immediately.