CVE-2026-93642 in Collaboration Suite
Summary
by MITRE • 09/25/2026
An unauthenticated sender can forge a share notification that triggers stored XSS when a signed-in Zimbra Modern recipient clicks Accept Share, allowing the attacker to access mailbox data and act as the victim.
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Analysis
by VulDB Data Team • 09/25/2026
The vulnerability described involves a critical security flaw within the Zimbra collaboration suite, specifically affecting its modern web client interface regarding file sharing mechanisms. This issue stems from an insufficient validation of input parameters associated with share notification payloads. An unauthenticated attacker can craft a malicious request that mimics a legitimate share notification without possessing valid authentication credentials for the target system. The core technical flaw lies in the server-side processing and subsequent rendering of these notifications, where user-supplied data is not adequately sanitized before being embedded into the HTML context presented to the recipient. This lack of proper output encoding or input validation allows for the injection of arbitrary JavaScript code, which constitutes a Stored Cross-Site Scripting (XSS) vulnerability. The persistence aspect of this flaw means that the malicious script remains stored on the server as part of the share notification data structure until it is retrieved and executed by a victim user.
The operational impact of this vulnerability is severe due to its interaction with authenticated sessions. While the initial trigger requires an unauthenticated sender, the exploitation phase relies entirely on the actions of a signed-in recipient. When a legitimate user receives the forged share notification and clicks the Accept Share button within their active Zimbra session, the browser executes the injected malicious script in the context of that authenticated domain. This execution environment grants the attacker full access to the victim's mailbox data, including emails, contacts, and stored files. Furthermore, because the script runs with the privileges of the logged-in user, it can perform actions on behalf of the victim, such as sending phishing emails to their contacts, modifying settings, or exfiltrating sensitive information directly to an external server controlled by the attacker. This effectively bypasses authentication controls for the specific action of accepting shares, turning a simple notification feature into a vector for complete account compromise and data breach.
From a classification perspective, this vulnerability aligns with CWE-79, which defines Improper Neutralization of Input During Web Page Generation commonly known as Cross-site Scripting (XSS). Specifically, it represents Stored XSS because the malicious payload is persisted on the target server rather than being passed via URL parameters or headers alone. In terms of adversary tactics and techniques, this exploit maps to ATT&CK technique T1059, Command and Scripting Interpreter, specifically JavaScript execution within a browser environment. It also relates to T1204, User Execution, as it requires the victim to interact with a malicious link or button (Accept Share) to trigger the payload. The attack chain demonstrates how social engineering elements combined with technical flaws in web application logic can lead to significant security breaches.
Mitigation strategies must address both immediate remediation and long-term architectural improvements. Administrators should apply vendor-provided patches immediately if available, as Zimbra typically releases updates to fix such critical vulnerabilities in their modern client components. In the interim, restricting access to share notification endpoints or implementing strict Content Security Policy (CSP) headers can help mitigate the impact by preventing unauthorized script execution even if XSS is attempted. Additionally, enforcing multi-factor authentication adds a layer of defense against account takeover resulting from credential theft via this vector. From a development standpoint, rigorous input validation and output encoding must be implemented for all data rendered in HTML contexts to prevent injection attacks. Regular security audits focusing on web application logic flaws are essential to identify similar vulnerabilities before they can be exploited by malicious actors seeking access to sensitive organizational data.