CVE-2026-93639 in Collaboration Suite
Summary
by MITRE • 10/23/2026
A missing authorization vulnerability in Zimbra Collaboration Suite (ZCS) allows a delegated administrator with no explicit administrative grants to overwrite global Zimlet configuration through ConfigureZimletRequest. The uploaded configuration can also add an attacker-controlled domain to the proxy allowlist of the default class of service. If a signed-in user in that class opens a crafted /service/proxy URL, Zimbra serves attacker-controlled HTML under its own origin. The resulting JavaScript can read mailbox data and perform authenticated actions as the victim. Exploitation requires a delegated-administrator account and access to the admin SOAP service; the browser compromise additionally requires the victim to open the crafted URL. ZCS 10.1.16 and 10.1.20 are affected.
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Analysis
by VulDB Data Team • 10/23/2026
The vulnerability described represents a critical authorization bypass within the Zimbra Collaboration Suite, specifically affecting versions such as 10.1.16 and 10.1.20. This flaw stems from an insufficient access control mechanism in the ConfigureZimletRequest API endpoint. In a properly secured environment, delegated administrators are granted specific subsets of administrative privileges to manage certain aspects of the system without possessing full root-level or global administrator rights. However, this vulnerability allows a user with only basic delegated admin status to execute operations that should be restricted to higher-privilege accounts. The core technical flaw lies in the server's failure to validate whether the requesting account possesses the necessary explicit administrative grants before processing requests intended to modify global configurations. This misconfiguration effectively elevates the privileges of an attacker who has obtained a low-level delegated admin account, allowing them to manipulate system-wide settings that impact all users within specific classes of service.
The operational impact of this vulnerability is severe due to its potential for cross-site scripting and data exfiltration through proxy abuse. By exploiting the missing authorization check, an attacker can overwrite global Zimlet configurations. A particularly dangerous consequence of this manipulation is the ability to add an attacker-controlled domain to the proxy allowlist associated with the default class of service. The Zimbra proxy mechanism is designed to serve content from external domains under the origin of the Zimbra server when accessed through specific URLs, a feature often used for legitimate integrations but easily weaponized in this context. When a victim user who belongs to the affected class of service accesses a crafted URL pointing to /service/proxy and targeting the attacker-controlled domain, the browser interprets the served content as originating from the trusted Zimbra origin rather than the malicious external site. This breaks the same-origin policy, which is fundamental to web security, allowing any JavaScript embedded in the served HTML to interact freely with the victim's active session on the Zimbra platform.
The exploitation chain requires two distinct phases: initial access and browser compromise. The attacker must first obtain credentials for a delegated administrator account that lacks explicit administrative grants but has sufficient permissions to reach the admin SOAP service. Once authenticated, the attacker submits the malicious ConfigureZimletRequest to inject their domain into the proxy allowlist. This step does not require user interaction beyond the initial authentication of the attacker's own session. The second phase involves social engineering or another vector to lure a victim from the targeted class of service into opening the crafted URL in their browser while logged into Zimbra. Upon loading, the malicious HTML executes within the context of the trusted origin, granting it unrestricted access to read sensitive mailbox data, such as emails and contacts, and perform authenticated actions on behalf of the user, including sending messages or modifying settings. This effectively results in a complete compromise of the victim's account confidentiality and integrity without requiring any browser-specific vulnerabilities beyond standard web application logic flaws.
From a classification perspective, this vulnerability aligns with CWE-269, which denotes Improper Privilege Control, as it involves an actor obtaining privileges they are not explicitly authorized to have. It also relates closely to CWE-862, Missing Authorization, where the software does not perform the correct authorization check before allowing access to a resource or function. In terms of offensive security frameworks like MITRE ATT&CK, this behavior maps to T1078 Valid Accounts, as it relies on legitimate but misconfigured credentials, and potentially T1534 Internal Spearphishing if used for lateral movement within an organization after initial compromise. The ability to serve content under a trusted origin also touches upon concepts related to cross-origin resource sharing abuses and proxy-based attacks, emphasizing the risk of trusting internal proxies without rigorous validation of input parameters.
Mitigation strategies must address both immediate remediation and long-term architectural improvements. The primary defense is applying vendor-provided patches that correct the authorization logic in the ConfigureZimletRequest endpoint for affected versions like 10.1.16 and 10.1.20. Administrators should ensure their systems are updated to a version where this privilege escalation path has been closed. In environments where patching is not immediately feasible, network-level controls can help mitigate the risk by restricting access to the admin SOAP service from untrusted networks or IP addresses. Additionally, implementing strict monitoring for unusual configuration changes made by delegated administrator accounts can aid in early detection of exploitation attempts. Organizations should also review their proxy allowlist configurations regularly to ensure that no unauthorized domains are permitted, and consider disabling unnecessary Zimlets that might expose complex configuration surfaces. Finally, enforcing multi-factor authentication on all administrative accounts reduces the likelihood of credential theft leading to this type of privilege escalation, adding a critical layer of defense against initial access.