CVE-2018-9990 in Server
Summary
by MITRE
In Zulip Server versions before 1.7.2, there was an XSS issue with stream names in topic typeahead.
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Analysis
by VulDB Data Team • 01/25/2020
The vulnerability CVE-2018-9990 represents a cross-site scripting flaw in Zulip Server versions prior to 1.7.2 that specifically affects the topic typeahead functionality when processing stream names. This issue arises from insufficient input validation and output encoding mechanisms within the web application's user interface components. The vulnerability is classified under CWE-79 which defines cross-site scripting as a weakness where an application incorporates untrusted data into web pages without proper validation or escaping, allowing attackers to inject malicious scripts that execute in the context of other users' browsers.
The technical implementation of this vulnerability occurs within the topic typeahead feature where stream names are dynamically rendered in dropdown menus or auto-complete suggestions. When a malicious user creates a stream with specially crafted HTML or JavaScript code embedded within the stream name, this content gets improperly rendered in the typeahead interface without appropriate sanitization. The flaw exists because the application fails to properly encode or escape special characters that could be interpreted as HTML or JavaScript when the stream name is displayed in the user interface. This allows an attacker to inject malicious scripts that execute when other users interact with the typeahead functionality, potentially leading to session hijacking, data theft, or further exploitation of the compromised user sessions.
The operational impact of this vulnerability extends beyond simple script execution as it can enable sophisticated attack vectors within collaborative environments like Zulip's chat platform. An attacker who gains the ability to create streams with malicious content can potentially steal session cookies, redirect users to phishing sites, or execute arbitrary code in the context of other users' browsers. The vulnerability is particularly concerning in enterprise environments where Zulip Server serves as a communication platform for sensitive business discussions and where users may have elevated privileges. The attack requires minimal privileges to exploit since the vulnerability exists in the display layer rather than requiring administrative access to the server itself, making it accessible to any user who can create or modify stream names.
Mitigation strategies for CVE-2018-9990 primarily involve upgrading to Zulip Server version 1.7.2 or later, which includes proper input sanitization and output encoding fixes for stream names in the topic typeahead functionality. Organizations should also implement additional defensive measures including content security policy headers to limit script execution, regular security audits of user-generated content, and monitoring for suspicious stream creation activities. The vulnerability aligns with ATT&CK technique T1059.001 for command and scripting interpreter and T1566.001 for spearphishing attachment, as attackers could leverage this vulnerability to establish persistent access through malicious scripts injected into the chat environment. Security teams should also consider implementing web application firewalls and input validation rules to prevent similar issues in other components of the application stack, as this represents a common pattern of insufficient output encoding that affects many web applications.