CVE-2026-5429 Overview
CVE-2026-5429 is a Cross-Site Scripting (XSS) vulnerability affecting the Kiro Agent webview component in Kiro IDE. The vulnerability stems from unsanitized input during web page generation, which allows a remote unauthenticated threat actor to execute arbitrary code through a crafted color theme name. Exploitation requires the local user to open a malicious workspace and trust it when prompted.
Critical Impact
Remote attackers can achieve arbitrary code execution on systems running vulnerable versions of Kiro IDE by exploiting improper input sanitization in the webview component.
Affected Products
- Kiro IDE versions prior to 0.8.140
- Kiro Agent webview component
Discovery Timeline
- April 2, 2026 - CVE-2026-5429 published to NVD
- April 2, 2026 - Last updated in NVD database
Technical Details for CVE-2026-5429
Vulnerability Analysis
This vulnerability is classified as CWE-79 (Improper Neutralization of Input During Web Page Generation), commonly known as Cross-Site Scripting (XSS). The Kiro Agent webview fails to properly sanitize user-controlled input when processing color theme names, creating an injection point that enables arbitrary code execution.
The attack requires local access, meaning the attacker must convince a victim to open a malicious workspace. However, once the workspace is opened and trusted by the user, the attacker can execute arbitrary code with high impact to confidentiality, integrity, and availability of the affected system. The vulnerability requires user interaction in the form of trusting the workspace when prompted.
Root Cause
The root cause of this vulnerability lies in insufficient input validation within the Kiro Agent webview's handling of color theme names. When a workspace is loaded, theme-related configuration data is processed without adequate sanitization, allowing specially crafted payloads embedded in theme names to be executed as code within the webview context.
Attack Vector
The attack vector requires a threat actor to create a malicious workspace containing a crafted color theme name with embedded malicious code. The attack flow proceeds as follows:
- The attacker creates a workspace with a malicious color theme name containing XSS payload
- The attacker distributes or shares this workspace with potential victims
- When a victim opens the workspace in Kiro IDE, they are prompted to trust it
- If the user trusts the workspace, the unsanitized theme name is processed by the Kiro Agent webview
- The malicious payload executes, allowing arbitrary code execution on the victim's system
The vulnerability manifests in the webview's theme processing functionality where user-supplied input is rendered without proper sanitization. Technical details can be found in the AWS Security Bulletin 2026-012 and the Kiro.dev IDE Patch 0.8.140 changelog.
Detection Methods for CVE-2026-5429
Indicators of Compromise
- Presence of unusual or obfuscated strings in workspace color theme configuration files
- Unexpected JavaScript execution or network connections originating from Kiro IDE processes
- Anomalous workspace configuration files containing encoded payloads in theme name fields
Detection Strategies
- Monitor for suspicious workspace files being opened with unusually long or encoded theme names
- Implement file integrity monitoring for Kiro IDE configuration directories
- Analyze workspace JSON/configuration files for potential XSS payloads before opening
Monitoring Recommendations
- Enable logging for Kiro IDE process activity and webview operations
- Monitor network connections initiated by Kiro IDE for unexpected outbound traffic
- Track workspace trust events and correlate with subsequent system behavior changes
How to Mitigate CVE-2026-5429
Immediate Actions Required
- Upgrade Kiro IDE to version 0.8.140 or later immediately
- Avoid opening workspaces from untrusted sources until the patch is applied
- Do not trust workspaces when prompted unless the source is verified and legitimate
- Review recently opened workspaces for potentially malicious theme configurations
Patch Information
The vendor has released a patch in Kiro IDE version 0.8.140 that addresses this vulnerability by implementing proper input sanitization for color theme names in the Kiro Agent webview. Users should upgrade to this version or later to remediate the vulnerability. Detailed patch information is available in the Kiro.dev IDE Patch 0.8.140 changelog.
Workarounds
- Exercise extreme caution when opening workspaces from unknown or untrusted sources
- Deny trust prompts for workspaces unless absolutely necessary and the source is verified
- Consider using network segmentation to limit potential impact if exploitation occurs
- Implement application allowlisting to restrict code execution from the Kiro IDE process
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
