CVE-2018-3780 in Nextcloud Server
Summary
by MITRE
A missing sanitization of search results for an autocomplete field in NextCloud Server <13.0.5 could lead to a stored XSS requiring user-interaction. The missing sanitization only affected user names, hence malicious search results could only be crafted by authenticated users.
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Analysis
by VulDB Data Team • 03/15/2020
The vulnerability identified as CVE-2018-3780 represents a critical stored cross-site scripting weakness within NextCloud Server versions prior to 13.0.5. This flaw specifically targets the autocomplete functionality's search results handling mechanism, creating a persistent security risk that requires user interaction to exploit. The vulnerability stems from inadequate input sanitization processes that fail to properly filter or escape user-provided data before it is stored and subsequently rendered in the autocomplete interface. The security implications are particularly concerning because the flaw enables malicious actors to inject persistent XSS payloads that can affect other users who interact with the compromised autocomplete functionality.
The technical nature of this vulnerability aligns with CWE-79, which specifically addresses cross-site scripting flaws in web applications. The flaw manifests as a missing sanitization step in the data processing pipeline where user names are not properly escaped or filtered before being stored in the system's autocomplete database. This creates a condition where authenticated users can craft malicious search terms containing XSS payloads that persist within the system. The requirement for user interaction indicates that the vulnerability cannot be exploited automatically, but rather depends on legitimate users performing search operations that trigger the malicious autocomplete results. This interaction requirement reduces the attack surface but does not eliminate the threat entirely, as social engineering or privilege escalation scenarios could still facilitate exploitation.
The operational impact of CVE-2018-3780 extends beyond simple data corruption or unauthorized access, as it enables attackers to execute arbitrary JavaScript code within the context of other users' browsers. When victims interact with the compromised autocomplete functionality, their browsers execute the malicious payloads, potentially leading to session hijacking, data theft, privilege escalation, or redirection to malicious sites. The fact that the vulnerability only affects user names suggests that the attack vector is limited to the user management and authentication aspects of NextCloud, but the potential for privilege abuse remains significant. This vulnerability particularly affects organizations relying on NextCloud for collaborative environments where multiple users interact with shared autocomplete features, creating a cascading risk that could compromise entire user bases.
Mitigation strategies for this vulnerability require immediate patching of NextCloud Server installations to version 13.0.5 or later, which contains the necessary sanitization fixes. Organizations should also implement additional defensive measures including input validation at multiple layers, regular security assessments of web application components, and monitoring for anomalous search patterns that might indicate malicious activity. The ATT&CK framework categorizes this vulnerability under T1059.007 for command and scripting interpreter, as the XSS payload execution could enable attackers to establish command execution capabilities. Network administrators should consider implementing web application firewalls to detect and block suspicious autocomplete payloads, while security teams should conduct comprehensive penetration testing to identify similar sanitization gaps in other application components. The vulnerability demonstrates the critical importance of proper input validation and output encoding in web applications, particularly in collaborative environments where user-generated content processing is prevalent.