CVE-2025-53543 is a medium-severity stored Cross-Site Scripting (XSS) vulnerability affecting versions of the Kestra event-driven orchestration platform prior to 0.22.0. The vulnerability arises from improper neutralization of input during web page generation, specifically in the "Overview" tab of the execution interface. When Kestra processes HTTP responses, it fails to adequately sanitize or encode certain inputs before rendering them in the web UI, allowing an attacker to inject malicious scripts that are stored and subsequently executed in the context of users viewing the affected page. This stored XSS flaw can lead to the execution of arbitrary JavaScript code within the victim's browser session. According to the CVSS v3.1 vector (CVSS:3.1/AV:L/AC:L/PR:H/UI:R/S:U/C:H/I:N/A:N), exploitation requires local access (AV:L), low attack complexity (AC:L), high privileges (PR:H), and user interaction (UI:R). The impact primarily affects confidentiality, enabling attackers to steal sensitive information accessible in the browser context, such as session tokens or other data. Integrity and availability are not directly impacted. The vulnerability has been addressed in Kestra version 0.22.0, and no known exploits are currently reported in the wild. Given Kestra's role as an orchestration platform, this vulnerability could be leveraged by insiders or attackers with elevated privileges to escalate their access or perform reconnaissance within the environment.

For European organizations using Kestra versions prior to 0.22.0, this vulnerability poses a risk of sensitive data exposure through malicious script execution in the web interface. Since exploitation requires high privileges and local access, the threat is more pronounced in environments where multiple users share access to the orchestration platform or where privilege boundaries are weak. Confidentiality breaches could lead to leakage of orchestration workflows, execution details, or authentication tokens, potentially enabling further lateral movement or data exfiltration. Although the vulnerability does not directly affect system integrity or availability, the ability to execute scripts in the context of privileged users can facilitate secondary attacks. European organizations in sectors with stringent data protection requirements (e.g., finance, healthcare, critical infrastructure) must consider the risk of compliance violations if sensitive data is exposed. The medium severity rating reflects the limited attack surface but does not diminish the importance of timely patching, especially in multi-tenant or collaborative environments.

1. Upgrade Kestra to version 0.22.0 or later, where this stored XSS vulnerability is fixed. 2. Implement strict access controls to limit the number of users with high privileges on the Kestra platform, reducing the risk of exploitation. 3. Employ web application firewalls (WAFs) with custom rules to detect and block suspicious script injections targeting the Kestra UI. 4. Conduct regular security audits and code reviews focusing on input validation and output encoding in custom plugins or integrations with Kestra. 5. Educate users with access to the Kestra interface about the risks of interacting with untrusted content and the importance of reporting unusual behavior. 6. Monitor logs for anomalous activities related to the execution "Overview" tab or HTTP response handling that could indicate attempted exploitation. 7. Where possible, isolate the Kestra management interface within secure network segments to limit exposure to untrusted users.