CVE-2018-9987 in Server
Summary
by MITRE
In Zulip Server versions 1.5.x, 1.6.x, and 1.7.x before 1.7.2, there was an XSS issue with muting notifications.
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Analysis
by VulDB Data Team • 01/25/2020
The vulnerability CVE-2018-9987 represents a cross-site scripting flaw discovered in Zulip Server versions 1.5.x through 1.7.x prior to the 1.7.2 release. This issue specifically affected the notification muting functionality within the messaging platform, creating a potential attack vector that could be exploited by malicious actors to execute arbitrary code in the context of a victim's browser. The vulnerability stems from insufficient input validation and output encoding mechanisms within the notification management system, allowing attackers to inject malicious scripts through crafted muting parameters.
The technical exploitation of this vulnerability occurs when users interact with specially crafted notification muting requests that contain malicious script payloads. These payloads are typically embedded within URL parameters or form data used to configure notification preferences. When the vulnerable server processes these requests without proper sanitization, the malicious scripts become executable within the browser context of authenticated users. This flaw directly maps to CWE-79, which categorizes cross-site scripting vulnerabilities as weaknesses in input validation and output encoding. The vulnerability demonstrates a classic failure in implementing proper context-aware output encoding, particularly in web applications where user-supplied data is rendered back to the browser without adequate sanitization.
The operational impact of CVE-2018-9987 extends beyond simple script execution, as it could enable attackers to perform session hijacking, steal sensitive user data, or manipulate the Zulip interface to deceive users into performing unintended actions. Attackers could potentially leverage this vulnerability to gain access to private conversations, modify user preferences, or redirect users to malicious domains. The risk is particularly elevated in environments where users frequently interact with notification settings, as the attack surface increases with user engagement. From an adversarial perspective, this vulnerability aligns with ATT&CK technique T1059.007 for Command and Scripting Interpreter, as attackers could execute malicious scripts through the browser interface, and T1566 for Phishing, as users might be tricked into clicking malicious links that exploit this vulnerability.
Mitigation strategies for this vulnerability involve implementing comprehensive input validation and output encoding measures throughout the Zulip Server application. The most effective immediate solution is updating to version 1.7.2 or later, which includes proper sanitization of user inputs used in notification muting functionality. Organizations should also implement Content Security Policy headers to limit script execution, employ proper input validation routines that filter or escape special characters, and conduct regular security assessments of web applications. Additionally, implementing web application firewalls and monitoring for suspicious parameter patterns can help detect and prevent exploitation attempts. The vulnerability highlights the critical importance of maintaining up-to-date software versions and demonstrates the necessity of comprehensive security testing, particularly for features that handle user-supplied data in web applications.