CVE-2018-20160 in Zimbra Collaboration Suite
Summary
by MITRE
ZxChat (aka ZeXtras Chat), as used for zimbra-chat and zimbra-talk in Synacor Zimbra Collaboration Suite 8.7 and 8.8 and in other products, allows XXE attacks, as demonstrated by a crafted XML request to mailboxd.
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Analysis
by VulDB Data Team • 09/25/2023
The vulnerability identified as CVE-2018-20160 affects ZxChat components within the Synacor Zimbra Collaboration Suite versions 8.7 and 8.8, as well as other affected products. This issue represents a critical security flaw that enables external XML entity attacks, allowing attackers to exploit the system through malformed XML requests processed by the mailboxd service. The vulnerability specifically targets the zimbra-chat and zimbra-talk modules, which are integral parts of the Zimbra Collaboration Suite's communication infrastructure. The flaw exists in how the system handles XML data processing, creating an avenue for malicious actors to potentially access sensitive information or compromise the underlying system. This vulnerability is particularly concerning because it affects core communication services that are fundamental to enterprise email and collaboration platforms.
The technical implementation of this vulnerability stems from insufficient input validation and sanitization within the XML processing pipeline of the affected Zimbra components. When the mailboxd service receives crafted XML requests containing external entity references, it fails to properly restrict or disable external entity loading, allowing attackers to reference external resources or execute malicious payloads. This weakness directly maps to CWE-611, which describes improper restriction of XML external entity reference, a classification that encompasses various XML injection vulnerabilities. The vulnerability enables attackers to perform server-side request forgery attacks, potentially leading to unauthorized data access, internal network reconnaissance, or even remote code execution depending on the system configuration and available resources. The attack vector is particularly dangerous because it can be executed through standard web-based interfaces that are commonly exposed to external networks.
The operational impact of this vulnerability extends beyond simple data theft or service disruption. Organizations using affected Zimbra versions face significant risks including unauthorized access to internal email systems, potential lateral movement within network environments, and exposure of sensitive corporate communications. The vulnerability can be exploited to extract user credentials, access confidential emails, or gain insights into internal system architecture through information disclosure attacks. Security teams must consider that this vulnerability could be leveraged as a stepping stone for more sophisticated attacks, potentially enabling privilege escalation or persistent access to the compromised environment. The widespread adoption of Zimbra Collaboration Suite makes this vulnerability particularly dangerous, as numerous enterprises may be affected simultaneously, creating a substantial attack surface for threat actors.
Organizations should implement immediate mitigations including disabling external entity loading in XML parsers, implementing strict input validation for all XML processing components, and applying available security patches from Synacor. Network segmentation and monitoring of XML-based traffic can help detect exploitation attempts, while regular security assessments should verify that no unauthorized external entity references are being processed. The vulnerability demonstrates the importance of proper XML security configuration and aligns with ATT&CK technique T1213.002, which covers data from information repositories, suggesting that exploitation may involve accessing stored data through compromised XML processing services. Additionally, organizations should consider implementing web application firewalls that can detect and block malicious XML payloads, and establish incident response procedures specifically tailored to address XML injection vulnerabilities in collaboration platforms.