CVE-2016-9924 in Zimbra Collaboration
Summary
by MITRE
Zimbra Collaboration Suite (ZCS) before 8.7.4 allows remote attackers to conduct XML External Entity (XXE) attacks.
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Analysis
by VulDB Data Team • 02/03/2020
The vulnerability identified as CVE-2016-9924 affects the Zimbra Collaboration Suite (ZCS) version 8.7.4 and earlier, representing a critical security flaw that enables remote attackers to execute XML External Entity (XXE) attacks against affected systems. This vulnerability resides within the web application layer of Zimbra's architecture, specifically impacting how the system processes XML data inputs. The XXE vulnerability stems from insufficient input validation and sanitization of XML documents, allowing malicious actors to manipulate the XML parser behavior and potentially access internal system resources or perform unauthorized operations. The flaw exists in the core XML processing functionality that handles various administrative and user-facing operations within the Zimbra platform, making it a significant threat vector for attackers seeking to compromise email services and associated infrastructure.
The technical exploitation of this XXE vulnerability occurs when the Zimbra system receives malformed XML input through various interfaces including web services, API endpoints, or administrative functions. Attackers can craft malicious XML payloads that reference external entities or internal system resources, causing the XML parser to resolve these references and potentially disclose sensitive information, perform server-side requests, or even execute arbitrary commands depending on the underlying system configuration. The vulnerability is particularly dangerous because it can be leveraged to access internal network resources that would normally be protected by firewalls, as the XML parser may attempt to resolve external entities from internal IP addresses or file systems. This type of attack falls under the CWE-611 category, which specifically addresses XXE vulnerabilities in XML parsers, and aligns with ATT&CK technique T1213.002 for data from information repositories, as attackers can extract sensitive data through these malformed XML requests.
The operational impact of CVE-2016-9924 extends beyond simple information disclosure, as successful exploitation could lead to complete system compromise and unauthorized access to email communications, user data, and administrative controls. Organizations using affected Zimbra versions face significant risks including potential data breaches, unauthorized access to internal systems, and service disruption. The vulnerability affects the core functionality of email services and could be exploited to gain access to user credentials, email content, and system configurations. Additionally, attackers might use this vulnerability as a stepping stone for further attacks within the network infrastructure, potentially leading to lateral movement and escalation of privileges. The attack surface is broad since Zimbra serves as a central communication platform for many organizations, making this vulnerability particularly attractive to threat actors seeking persistent access to enterprise networks.
Mitigation strategies for CVE-2016-9924 primarily involve upgrading to Zimbra Collaboration Suite version 8.7.4 or later, which includes proper XML parser configuration and input validation measures. Organizations should implement comprehensive XML input sanitization and ensure that all external entity declarations are disabled or properly restricted within the XML processing components. Network segmentation and firewall rules should be configured to limit access to Zimbra services, particularly restricting access to administrative interfaces and internal system resources. Security monitoring should be enhanced to detect unusual XML processing patterns or attempts to access external resources through the XML parser. Additionally, implementing proper access controls, regular security assessments, and vulnerability scanning should be part of the overall security posture to prevent exploitation of similar vulnerabilities. The remediation process should include thorough testing of the updated system to ensure that legitimate XML processing functionality remains intact while eliminating the XXE attack vectors. Organizations should also consider implementing web application firewalls and input validation controls specifically designed to prevent XXE attacks, as these provide additional layers of protection against such vulnerabilities.