CVE-2024-36624 identifies a Cross Site Scripting (XSS) vulnerability in Zulip version 8.3, specifically within the construct_copy_div function located in the copy_and_paste.js script. This vulnerability arises due to improper sanitization or escaping of user-supplied input that is processed by this function, allowing an attacker to inject malicious JavaScript code. When a victim interacts with the affected functionality, the injected script executes in their browser context, potentially leading to unauthorized actions such as session hijacking, credential theft, or manipulation of displayed content. The vulnerability requires an attacker to have low privileges (PR:L) and necessitates user interaction (UI:R), such as clicking or pasting content, to trigger the exploit. The CVSS v3.1 base score is 6.1, reflecting a medium severity level, with attack vector being network (AV:N), low attack complexity (AC:L), partial confidentiality and integrity impact (C:L/I:L), no availability impact (A:N), and scope changed (S:C), indicating that the vulnerability affects components beyond the initially vulnerable component. No patches or known exploits are currently available, but the vulnerability is publicly disclosed and should be addressed promptly. The CWE classification is CWE-79, which corresponds to improper neutralization of input during web page generation leading to XSS.

The primary impact of this vulnerability is the potential compromise of user confidentiality and integrity within Zulip 8.3 deployments. Attackers exploiting this XSS flaw can execute arbitrary scripts in the context of authenticated users, potentially stealing session tokens, credentials, or other sensitive data accessible via the browser. They may also manipulate or deface content displayed to users, undermining trust and data integrity. While availability is not directly affected, successful exploitation could lead to secondary attacks or social engineering campaigns. Organizations using Zulip for internal or external communications risk exposure of sensitive information and potential disruption of secure collaboration. The scope change in the CVSS vector suggests that the vulnerability could affect multiple components or users beyond the initially targeted area, increasing the risk surface. Given the requirement for user interaction and low privileges, exploitation is feasible but requires some user involvement, limiting automated mass exploitation. However, targeted attacks against high-value users or organizations remain a concern.

To mitigate CVE-2024-36624, organizations should implement several specific measures beyond generic advice: 1) Immediately audit and restrict user input in Zulip, especially in areas involving copy and paste operations, to ensure no untrusted content is processed without proper sanitization. 2) Review and enhance the construct_copy_div function in copy_and_paste.js to apply robust output encoding and input validation, preventing script injection. 3) Employ Content Security Policy (CSP) headers to restrict the execution of unauthorized scripts within Zulip web clients, limiting the impact of potential XSS payloads. 4) Educate users about the risks of interacting with untrusted content or links within Zulip messages to reduce the likelihood of triggering the vulnerability. 5) Monitor Zulip vendor communications for official patches or updates and prioritize their deployment as soon as they become available. 6) Consider deploying web application firewalls (WAFs) with rules tailored to detect and block XSS attempts targeting Zulip. 7) Conduct regular security testing, including penetration testing focused on XSS vectors, to identify and remediate similar issues proactively. These steps collectively reduce the attack surface and limit the potential damage from exploitation.