CVE-2018-3764 in Contacts
Summary
by MITRE
In Nextcloud Contacts before 2.1.2, a missing sanitization of search results for an autocomplete field could lead to a stored XSS requiring user-interaction. The missing sanitization only affected group names, hence malicious search results could only be crafted by privileged users like admins or group admins.
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Analysis
by VulDB Data Team • 02/25/2020
The vulnerability identified as CVE-2018-3764 affects Nextcloud Contacts versions prior to 2.1.2 and represents a stored cross-site scripting flaw that requires user interaction to exploit. This vulnerability specifically targets the autocomplete functionality within the contacts application, where search results are not properly sanitized before being rendered back to users. The security flaw stems from inadequate input validation and output sanitization practices within the application's search handling mechanisms. The vulnerability is classified under CWE-79 as a failure to sanitize or incorrectly sanitize output data, making it a classic stored XSS vulnerability where malicious payloads can be persisted and executed when users interact with the affected search results.
The technical implementation of this vulnerability occurs within the autocomplete field of the contacts application where group names are processed without proper sanitization. When privileged users such as administrators or group administrators create malicious group names containing script tags or other malicious code, these payloads are stored in the application's database. The vulnerability specifically affects group names because the sanitization process was implemented only for certain input fields while leaving group name processing unaddressed. This creates a scenario where a malicious actor with appropriate privileges can inject malicious content that will execute when other users view or interact with the autocomplete suggestions. The requirement for user interaction means that the vulnerability cannot be exploited automatically but requires a user to trigger the vulnerable autocomplete functionality.
The operational impact of this vulnerability is significant within Nextcloud environments where group management is common and privileged users exist. Attackers with administrative or group administrator privileges can craft malicious group names that contain XSS payloads, which then get executed when other users browse contacts or use autocomplete features. This creates a persistent threat vector that can be used to steal session cookies, redirect users to malicious sites, or perform other malicious actions on behalf of authenticated users. The vulnerability affects the confidentiality and integrity of the Nextcloud environment as it allows for unauthorized code execution within the context of user sessions. The attack vector is particularly concerning because it leverages legitimate administrative functionality to create a backdoor that can be triggered by any user who interacts with the vulnerable autocomplete feature.
The mitigation for CVE-2018-3764 involves updating Nextcloud Contacts to version 2.1.2 or later where the sanitization issue has been addressed. Organizations should also implement proper input validation and output sanitization practices throughout their applications, particularly in fields that handle user-provided data that will be displayed to other users. The fix typically involves implementing proper HTML escaping or encoding of all user-supplied content before storing or rendering it in web interfaces. Security practitioners should also consider implementing content security policies to add additional defense-in-depth measures. This vulnerability aligns with ATT&CK technique T1059.001 for command and scripting interpreter and T1546.008 for exploit for privilege escalation through malicious code injection, making it a critical vulnerability for organizations to address promptly. The incident highlights the importance of comprehensive security testing including input validation and output sanitization testing for web applications.