# Urgent Update Required: Critical XSS Vulnerability in Zimbra's Classic Web Client

*Published July 13, 2026*
*Source: [https://thehackernews.com/2026/07/critical-zimbra-flaw-could-let-crafted_0483473395.html](https://thehackernews.com/2026/07/critical-zimbra-flaw-could-let-crafted_0483473395.html)*

## Executive Summary

Zimbra has identified a critical stored XSS vulnerability in its Classic Web Client that could allow attackers to execute malicious code via crafted emails. Users are urged to update to version 10.1.19 to protect against potential exploitation.

## Article

Zimbra has issued an urgent call for its users to update the Classic Web Client to address a critical security vulnerability. This flaw, identified as a stored cross-site scripting (XSS) issue, can enable attackers to execute arbitrary code through specially crafted emails. Although a CVE identifier has not been assigned yet, the potential impact is significant. When a user opens a maliciously crafted email, the script can run, compromising mailbox information, session data, and account settings.

XSS vulnerabilities like this occur when an application displays untrusted data on a web page without proper validation. This allows malicious JavaScript to be injected into victims' browsers, leading to session hijacking, credential theft, and other security breaches. Stored XSS is particularly dangerous because the malicious script is saved on the server, affecting anyone who visits the compromised page.

While there is no current evidence that this vulnerability is being exploited in the wild, Zimbra's history with XSS flaws suggests immediate attention is necessary. Past incidents, including a zero-day attack targeting Brazilian military systems last year, highlight the serious risks posed by these vulnerabilities. Zimbra users should update to the latest Zimbra Collaboration Suite version 10.1.19 to ensure optimal protection against potential threats.