CVE-2026-66824 in Lookyloo
Summary
by MITRE • 07/28/2026
A stored cross-site scripting vulnerability existed in the capture tree visualization page. The application embedded the serialized capture tree directly into an inline JavaScript block using the Jinja safe filter.
Because the tree data can contain values derived from captured and potentially attacker-controlled web content, a specially crafted value could prematurely terminate the surrounding <script> element and inject arbitrary HTML or JavaScript. The malicious code would execute in the browser of a user viewing the affected capture tree.
Successful exploitation could allow an attacker to perform actions using the victim’s authenticated session, access information available to the victim, or modify application data within the permissions of the affected user.
The patch removes the JSON data from the HTML document and retrieves it through a dedicated API endpoint. The client then processes the response using response.json(), preventing capture data from being interpreted as executable content within the original page’s HTML or JavaScript context.
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Analysis
by VulDB Data Team • 07/28/2026
This vulnerability represents a classic stored cross-site scripting flaw that emerged from improper handling of user-controllable data within web application markup. The issue occurred in a capture tree visualization page where serialized data was directly embedded into inline javascript blocks without proper sanitization. The application utilized the Jinja safe filter which, while intended to mark content as trusted, failed to account for the fact that captured data could contain attacker-controlled values that would break out of the expected html context and inject malicious code. This type of vulnerability falls under CWE-79 - Cross-site Scripting and specifically demonstrates how improper input validation can lead to code execution in victim browsers.
The technical exploitation mechanism relied on the predictable structure of html attribute handling combined with the lack of proper escaping for javascript contexts. When attacker-controlled values were included in the capture tree data, they could contain characters that would prematurely terminate html attributes or script blocks, allowing arbitrary javascript execution within the victim's browser session. The vulnerability essentially created a sandbox escape where untrusted data flowing through the application's serialization process became executable code. This attack vector operates at the intersection of CWE-1004 - Sensitive Cookie Without 'HttpOnly' flag and CWE-79, demonstrating how data flow issues can compound security weaknesses.
The operational impact of this vulnerability was significant as it provided attackers with authenticated access privileges equivalent to the victim user's permissions. Successful exploitation could enable session hijacking attacks where malicious actors could perform actions on behalf of victims, access sensitive information that the victim could view, or modify application data within the scope of the user's authorization level. This represents a critical threat in applications where users have varying permission levels, as attackers could potentially escalate privileges or access restricted functionality through this vector.
The remediation approach implemented addressed the core architectural issue by separating data from presentation layers through proper API design. Moving JSON data to dedicated endpoints and using response.json() processing eliminated the direct embedding of untrusted data into javascript contexts. This solution aligns with the principle of least privilege and proper input validation as outlined in the OWASP Top Ten security controls. The fix essentially implements a secure data handling pattern where client-side code fetches data through authenticated API calls rather than receiving it directly embedded within html documents, thereby preventing the injection attack surface that previously existed.
This vulnerability demonstrates how seemingly innocuous data processing patterns can create significant security risks when proper sanitization and context-aware escaping are not applied. The ATT&CK framework categorizes this under T1059 - Command and Scripting Interpreter and T1566 - Phishing, as the attack chain typically involves initial compromise through phishing or other delivery mechanisms followed by exploitation of such vulnerabilities to establish persistent access. Organizations should implement comprehensive input validation and output encoding strategies, particularly when dealing with user-generated content that may be displayed in web interfaces, and regularly audit their applications for similar patterns that could lead to stored XSS vulnerabilities.