CVE-2026-102139 in Email Protection Gateway
Summary
by MITRE • 10/01/2026
An authorization check in the large file exchange feature of Kiteworks Email Protection Gateway did not correctly establish that the requesting user was a party to the package being requested. An authenticated user of that optional feature could read the subject, message body, and attachments of packages they neither sent nor received.
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Analysis
by VulDB Data Team • 10/01/2026
The vulnerability identified in Kiteworks Email Protection Gateway represents a critical failure in access control logic within its large file exchange functionality. This component is designed to facilitate secure sharing of substantial data sets via email-adjacent mechanisms, requiring strict enforcement of permissions to ensure that only authorized participants can view or download shared content. The core technical flaw lies in the authorization check performed when a user requests access to a specific package. Instead of validating whether the authenticated session corresponds to an entity explicitly listed as either the sender or recipient of the targeted package, the system fails to verify this relationship adequately. Consequently, the application grants read access based on insufficient criteria, allowing any authenticated user with knowledge of the package identifier or URL to bypass intended restrictions and retrieve sensitive information belonging to other users.
From a technical perspective, this issue is classified as an Insecure Direct Object Reference (IDOR), which corresponds to CWE-639 in the Common Weakness Enumeration standard. The vulnerability stems from trusting client-supplied identifiers without performing server-side validation against the user's assigned permissions and relationships within the application database. By neglecting to cross-reference the requesting user's identity with the package ownership or membership records, the software exposes a classic broken access control scenario where horizontal privilege escalation is possible through parameter manipulation or enumeration of valid package IDs. This type of flaw often arises when developers assume that visibility into an object implies permission to interact with it, without implementing robust checks for actual entitlements associated with that specific resource instance.
The operational impact of this vulnerability is severe due to the nature of the data involved. Since authenticated users can read the subject line, message body, and attachments of packages they did not send or receive, there is a significant risk of unauthorized disclosure of confidential business information, personally identifiable information, or regulated data such as health records or financial details depending on the organization's usage patterns. Attackers who have obtained valid credentials for any user account within the system can potentially harvest sensitive communications from other departments or individuals by iterating through package identifiers if they are predictable or discoverable via error messages and API responses. This compromises the confidentiality integrity of the entire email protection gateway, undermining trust in the secure file transfer capabilities provided to employees and partners.
Mitigation strategies must address both immediate remediation and long-term architectural improvements. The primary fix involves patching the Kiteworks Email Protection Gateway software to correct the authorization logic so that it strictly verifies user membership or ownership before granting access to package contents. Administrators should ensure their systems are updated to the latest version provided by the vendor, which includes this security correction. In the interim, organizations should enforce strict password policies and multi-factor authentication to reduce the risk of credential theft leading to exploitation. Additionally, implementing network-level monitoring for unusual patterns in file exchange requests can help detect potential enumeration attacks where an attacker attempts to access multiple packages systematically. Regular audits of access control lists and adherence to the principle of least privilege will further strengthen the security posture against similar vulnerabilities aligned with MITRE ATT&CK technique T1078, which covers valid accounts being used for unauthorized access.