CVE-2026-10632 in Collaboration Suite
Summary
by MITRE • 10/23/2026
A reflected cross-site scripting vulnerability in the Classic Web Client of Zimbra Collaboration Suite (ZCS) allows an attacker to inject JavaScript through the packages parameter of the /h/rest document editor. The editor inserts package names into script attributes without HTML encoding. When combined with CVE-2026-50053, an attacker with an ordinary Zimbra account can supply their own authentication token and document identifiers in a URL and execute JavaScript in another signed-in user's Zimbra browser session when that user opens the URL. This permits reading mailbox data and performing authenticated actions as the victim. The issue affects ZCS 10.1.16 and was remediated in 10.1.17.
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Analysis
by VulDB Data Team • 10/23/2026
The vulnerability described represents a critical security flaw within the Classic Web Client of Zimbra Collaboration Suite, specifically affecting versions up to 10.1.16. This issue is classified as a reflected cross-site scripting (XSS) vulnerability that arises from improper input validation and output encoding in the /h/rest document editor endpoint. The core technical failure lies in how the application handles the packages parameter during REST API interactions. When user-supplied data for this parameter is processed, it is inserted directly into script attributes without undergoing proper HTML entity encoding or sanitization. This lack of encoding allows malicious JavaScript code to be embedded within the HTTP response and subsequently executed by the victim's browser upon rendering the page.
The operational impact of this vulnerability is significantly amplified when combined with a related authentication bypass flaw identified as CVE-2026-50053. While an XSS vulnerability typically requires social engineering or specific conditions to trigger, the combination with the authentication token manipulation creates a highly exploitable scenario for attackers holding standard user accounts. An attacker can craft a malicious URL containing their own forged authentication tokens and valid document identifiers. When this URL is accessed by another authenticated Zimbra user, the browser executes the injected script within the context of that victim's active session. This effectively allows the attacker to hijack the victim's session privileges without needing to steal credentials through traditional phishing or keylogging methods.
The consequences of successful exploitation are severe and directly compromise the confidentiality and integrity of the organization's communication infrastructure. Once the JavaScript is executed in the victim's browser, it can perform authenticated actions on behalf of that user. This includes reading sensitive mailbox data such as emails, contacts, and calendar entries, which violates core privacy expectations. Furthermore, the attacker gains the ability to send emails, modify settings, or delete messages, thereby compromising the integrity of the system. The attack vector is primarily web-based, leveraging the browser's trust in the domain context to bypass same-origin policy protections through script execution rather than data exfiltration via standard API calls alone.
From a classification perspective, this vulnerability aligns with CWE-79, which covers Improper Neutralization of Input During Web Page Generation commonly known as Cross-site Scripting. The specific mechanism involves reflected XSS where the malicious payload is provided in an HTTP request and immediately returned by the web application without being stored on the server side. In terms of adversary tactics, this aligns with MITRE ATT&CK techniques related to Client-side Injection and potentially Account Manipulation if used to escalate privileges or maintain persistence through session hijacking. The exploitation relies heavily on user interaction, specifically clicking a crafted link, which places it within the realm of social engineering-assisted attacks despite the technical sophistication required for token manipulation.
To mitigate this risk, organizations running Zimbra Collaboration Suite must ensure they have upgraded to version 10.1.17 or later where these issues are remediated. Immediate patching is essential as no reliable client-side workaround exists due to the nature of session hijacking and script execution in modern browsers. Administrators should also enforce strict Content Security Policy headers if not already implemented, although this serves primarily as a defense-in-depth measure rather than a primary fix for such fundamental input validation errors. Regular security audits focusing on REST API endpoints and document editors are recommended to identify similar patterns of improper encoding across other modules within the suite.