CVE-2018-3781 in Talk
Summary
by MITRE
A missing sanitization of search results for an autocomplete field in NextCloud Talk <3.2.5 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-2018-3781 represents a critical stored cross-site scripting flaw within NextCloud Talk version 3.2.4 and earlier, specifically affecting the autocomplete functionality used in search operations. This vulnerability resides in the application's handling of user-generated content within the autocomplete field, where insufficient input sanitization permits malicious payloads to be stored and subsequently executed when other users interact with the affected system. The flaw demonstrates characteristics of CWE-79 - Improper Neutralization of Input During Web Page Generation, which directly enables attackers to inject malicious scripts into web pages viewed by other users.
The technical implementation of this vulnerability stems from the application's failure to properly sanitize user names within the autocomplete search results. When authenticated users submit search queries containing malicious script code, the application stores these inputs without adequate filtering or encoding mechanisms. This stored data becomes part of the autocomplete suggestions that are later presented to other authenticated users during search operations. The requirement for user interaction means that victims must actively engage with the autocomplete functionality for the malicious script to execute, typically through clicking on a compromised search result or simply triggering the autocomplete dropdown. This design element significantly limits the attack surface compared to fully automated XSS vectors but still presents a substantial security risk within the application's trusted user environment.
The operational impact of this vulnerability extends beyond simple script execution, as it enables attackers to potentially escalate privileges, steal session cookies, perform unauthorized actions on behalf of victims, or redirect users to malicious websites. The stored nature of the XSS payload means that the attack can persist for extended periods, affecting multiple users over time without requiring repeated exploitation attempts. Given that the vulnerability specifically targets user names within autocomplete fields, attackers must first establish authenticated access to the system to craft malicious search results, which aligns with ATT&CK technique T1078 - Valid Accounts, as the attack requires legitimate user credentials. The requirement for authenticated access reduces the attack surface to insider threats or compromised accounts, but the potential for privilege escalation and data theft remains significant.
Mitigation strategies for this vulnerability should prioritize immediate patching to NextCloud Talk version 3.2.5 or later, which implements proper input sanitization and output encoding for autocomplete fields. Organizations should also implement additional defensive measures including enhanced monitoring of search functionality, regular security audits of user-generated content handling, and user education about the risks of interacting with suspicious autocomplete suggestions. The implementation of Content Security Policy (CSP) headers can provide additional protection layers against script execution, while proper input validation and output encoding should be enforced throughout the application's search and autocomplete components. Security teams should also consider implementing automated scanning tools to detect similar sanitization issues in other application components, as this vulnerability type frequently appears in web applications that handle user input in dynamic contexts. The fix implemented in version 3.2.5 demonstrates proper security practices including input validation, output encoding, and proper sanitization of user data before storage and retrieval, addressing the root cause identified in CWE-79 and preventing the conditions that enabled the stored XSS attack vector.