The vulnerability identified as CVE-2026-9255 affects AWS Kiro CLI before version 1.28.0. It is caused by missing input source validation in the tool authorization prompt, which allows a local attacker to bypass user approval and execute arbitrary tools or shell commands by supplying crafted content through stdin. This flaw corresponds to CWE-862 (Missing Authorization). The CVSS 3.1 base score is 7.8, reflecting high impact with local attack vector, low attack complexity, no privileges required, user interaction required, unchanged scope, and high impact on confidentiality, integrity, and availability. AWS has released a fixed version (1.28.0) and recommends upgrading to mitigate the vulnerability. The service is cloud-hosted, and AWS manages remediation accordingly.

Successful exploitation allows a local attacker to execute arbitrary tools or shell commands without user approval, potentially leading to full compromise of confidentiality, integrity, and availability of the affected system. This can result in unauthorized command execution and control over the Kiro CLI environment. No known exploits are currently reported in the wild.

AWS recommends upgrading to Kiro CLI version 1.28.0 or later, which includes a fix for this vulnerability. Since this is a cloud-hosted service, AWS manages remediation on their side. Users should follow the vendor advisory at https://aws.amazon.com/security/security-bulletins/2026-035-aws/ for the latest guidance and ensure their Kiro CLI installations are updated promptly.