Install Kiro IDE 0.8.140 Now to Prevent RCE from Malicious Color Theme Names in Trusted Workspaces

Remote attackers can execute arbitrary code on systems running vulnerable versions of the Kiro IDE by tricking users into opening workspaces with malicious color themes. This cross-site scripting flaw, identified as CVE-2026-5429, was addressed by AWS in version 0.8.140, released on April 2, 2026.

The vulnerability exists in the Kiro Agent webview component of the development environment. Before version 0.8.140, the system failed to sanitize input during web page generation. This oversight allowed unauthenticated threat actors to inject malicious scripts through crafted color theme names.

Context and Background

AWS describes Kiro IDE as an agentic development environment designed to help developers ship engineering work with AI agent assistance. The security bulletin classifies this issue as important and requiring attention. The flaw specifically impacts how the webview handles workspace color theme data.

Dhiraj Mishra discovered the vulnerability and collaborated with AWS through the coordinated disclosure process. AWS thanked Mishra for reporting the issue. The company published the advisory on April 2, 2026, at 11:30 AM PST.

Who Is Affected

Users of Kiro IDE versions prior to 0.8.140 are affected by this vulnerability. The attack requires a local user to open a workspace and trust it when prompted. Small-business owners and development teams using this IDE should verify their current version immediately.

Forked or derivative code bases may also be vulnerable if they have not incorporated the fixes from version 0.8.140. Organizations using custom builds should ensure they patch their code to include the new security measures provided by AWS.

What to watch

Monitor AWS security bulletins for updates on Kiro IDE and related agentic development tools. Check your current IDE version against the patched release notes. Verify that all developers in your organization have updated their environments.

Watch for any new advisories regarding webview components in development tools. Ensure your security monitoring systems can detect unusual script execution or unexpected behavior in IDE environments. Review access logs for any signs of unauthorized workspace openings.

What made it possible

This incident illustrates how unsanitized input in webview components can lead to remote code execution. Attackers exploit the trust users place in development environments by injecting malicious data through seemingly benign features like color themes. Teams usually face risks when applications process external input without proper validation. Check whether your development tools sanitize all user-supplied data before rendering it in webviews. This stage of intrusion allows attackers to gain initial access and execute arbitrary commands on the host system.

Background: Cross-site scripting (XSS)

To mitigate cross-site scripting, you must encode data before rendering it in the browser. Input validation is insufficient because it rarely covers all edge cases. Implement Content Security Policy headers to restrict script sources. Use framework auto-encoding features to prevent accidental injection of malicious code into your HTML responses.

Read the full guide: How to Mitigate Cross Site Scripting: A Risk-Based Approach

What to do and how to stay safe: AWS

• Update Kiro IDE to version 0.8.140 or later to apply the official security patch.
• Verify that all developers on your team have updated their IDE installations before opening new workspaces.
• Review any forked or custom versions of Kiro IDE to ensure they incorporate the latest security fixes.
• Monitor system logs for unusual script execution or unexpected behavior after opening workspaces from untrusted sources.

Step-by-step guide: How Security Advisories Drive Patch Decisions and Reduce Risk

General security guidance from the Shell Bulletin newsroom. It is not confirmed advice from the organisations named in this story.

Frequently asked questions

What is CVE-2026-5429?

CVE-2026-5429 is a cross-site scripting vulnerability in Kiro IDE that allows remote unauthenticated attackers to execute arbitrary code via malicious color theme names.

Which versions of Kiro IDE are affected?

All versions of Kiro IDE before 0.8.140 are affected by this vulnerability.

How can users protect themselves?

Users should upgrade to Kiro IDE version 0.8.140 or later and ensure any forked code is patched with the new fixes.