Bulletin ID: 2026-073-AWS
Scope: AWS
Content Type: Important (requires attention)
Publication Date: 08/04/2026 10:00 AM PDT

Description:

We have identified CVE-2026-18830 in the Amazon Bedrock AgentCore harness InvokeHarness API. This issue could allow an authenticated user to execute configured tools while bypassing model invocation and associated security controls. When the most recent message in an InvokeHarness request contained a tool-use content block, the agent event loop could dispatch the named tool directly, without model mediation.

Please note that potential impact was limited to the tools configured on a given harness. A harness with no configured tools could not execute any tool, and a harness with a restricted tool set was limited to that set.

Impacted versions: 

Amazon Bedrock AgentCore harness InvokeHarness API prior to July 31, 2026.

Resolution:

AWS added server-side input validation that rejects caller-supplied tool-use content blocks in the final message of an InvokeHarness request, before the request reaches the agent event loop. This issue has been fully addressed in the AWS-managed service.

Workarounds:

None required. The mitigation is applied automatically on the server side for all requests.

References:

• CVE-2026-18830

Acknowledgements:

We would like to thank Aviyam Ivgi and Hedi Ingber for reporting and collaborating on this issue through the coordinated issue disclosure process.

Please email aws-security@amazon.com with any security questions or concerns.