CVE-2018-10949 in Zimbra Collaboration
Summary
by MITRE
mailboxd in Zimbra Collaboration Suite 8.8 before 8.8.8; 8.7 before 8.7.11.Patch3; and 8.6 allows Account Enumeration by leveraging a Discrepancy between the "HTTP 404 - account is not active" and "HTTP 401 - must authenticate" errors.
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Analysis
by VulDB Data Team • 02/03/2020
The vulnerability identified as CVE-2018-10949 affects the mailboxd service within Zimbra Collaboration Suite across multiple versions including 8.8 before 8.8.8, 8.7 before 8.7.11.Patch3, and 8.6. This issue represents a significant account enumeration flaw that enables attackers to determine the existence of valid user accounts within the system through careful analysis of server response codes. The vulnerability stems from inconsistent error handling mechanisms that provide different HTTP status codes for various account states, creating a distinguishable pattern that can be exploited for reconnaissance purposes.
The technical flaw manifests when the mailboxd service responds with distinct HTTP status codes based on account conditions. Specifically, when an account is inactive, the system returns an HTTP 404 error code, whereas accounts that require authentication but exist within the system produce an HTTP 401 error. This discrepancy creates a predictable pattern that attackers can leverage to systematically test account existence by observing the response codes returned for different account identifiers. The vulnerability operates at the application layer and can be exploited through automated tools that iterate through potential usernames while monitoring response variations.
The operational impact of this vulnerability extends beyond simple reconnaissance as it provides attackers with a foundation for more sophisticated attacks including brute force authentication attempts, credential stuffing, and targeted phishing campaigns. An attacker who can enumerate valid accounts gains a significant advantage in launching further attacks against the system, as they now possess a list of potentially valid user accounts that can be targeted with various attack vectors. The vulnerability affects the confidentiality and integrity aspects of the system by exposing user account information that should remain private and protected from unauthorized discovery.
This vulnerability aligns with CWE-200, which addresses Information Exposure, and represents a specific instance of how inconsistent error handling can lead to unintended information disclosure. From an attacker perspective, this flaw maps to techniques described in the MITRE ATT&CK framework under the reconnaissance phase, specifically targeting credential access and privilege escalation tactics. The vulnerability demonstrates how seemingly minor implementation details in error handling can create significant security implications when they provide distinguishable responses that reveal system state information.
Organizations should implement immediate mitigations including standardizing error responses across all account states to prevent information leakage, implementing rate limiting and account lockout mechanisms to prevent automated enumeration attempts, and ensuring that all versions of Zimbra Collaboration Suite are updated to patched releases. The recommended approach involves configuring the system to return consistent error responses regardless of account status, thereby eliminating the distinguishable patterns that enable enumeration attacks. Additionally, network-level controls such as intrusion detection systems can be configured to monitor for suspicious patterns of account enumeration attempts, and regular security assessments should verify that error handling mechanisms do not inadvertently expose account information.