CVE-2024-36625 identifies a Cross Site Scripting (XSS) vulnerability in Zulip version 8.3, specifically within the replace_emoji_with_text function located in the ui_util.ts source file. This function is responsible for replacing emoji characters with their textual equivalents in the user interface. The vulnerability arises because the function does not properly sanitize or encode user-supplied input before rendering it in the browser context, allowing malicious scripts to be injected and executed. The flaw is categorized under CWE-79, which covers improper neutralization of input during web page generation. The CVSS 3.1 base score is 6.1, indicating a medium severity level. The vector string (AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N) reveals that the attack can be launched remotely over the network with low attack complexity, requires low privileges (authenticated user), and user interaction (clicking a malicious link or content). The scope is changed (S:C), meaning the vulnerability affects components beyond the initially vulnerable component, impacting confidentiality and integrity but not availability. No known exploits have been reported in the wild, and no official patches have been linked yet, suggesting that the vulnerability is newly disclosed. Zulip is a widely used open-source team chat platform, so the vulnerability could impact many organizations relying on it for internal communication.

The primary impact of this vulnerability is the potential for an attacker to execute arbitrary JavaScript in the context of a victim's browser session within Zulip. This can lead to theft of session cookies, enabling account takeover, unauthorized actions performed on behalf of the victim, and exposure of sensitive information, thus compromising confidentiality and integrity. Since the vulnerability requires authentication and user interaction, the attack surface is somewhat limited to users within the Zulip environment who can be tricked into interacting with malicious content. However, given Zulip's role as a collaboration platform, successful exploitation could facilitate lateral movement within organizations, espionage, or disruption of secure communications. The vulnerability does not affect availability directly but could degrade trust and operational security. Organizations worldwide using Zulip for team communication, especially those in sectors handling sensitive or regulated data, face increased risk if this vulnerability is exploited.

Organizations should immediately review their Zulip deployments and restrict access to trusted users while monitoring for suspicious activity. Since no official patch is currently linked, temporary mitigations include disabling or restricting the use of emoji replacement features or sanitizing inputs at the application or web server level using web application firewalls (WAFs) configured to detect and block XSS payloads targeting the vulnerable function. Administrators should enforce strict Content Security Policy (CSP) headers to limit script execution sources and reduce the impact of potential XSS attacks. User education is critical to avoid clicking on suspicious links or content within Zulip. Monitoring logs for unusual behavior and preparing to apply patches once released by Zulip developers is essential. Additionally, organizations should consider isolating Zulip instances and limiting integration with other critical systems until the vulnerability is remediated.