CVE-2016-7968 in KMail
Summary
by MITRE
KMail since version 5.3.0 used a QWebEngine based viewer that had JavaScript enabled. HTML Mail contents were not sanitized for JavaScript and included code was executed.
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Analysis
by VulDB Data Team • 10/12/2022
The vulnerability identified as CVE-2016-7968 represents a critical security flaw in KMail email client versions 5.3.0 and later, where the application utilized a QWebEngine based viewer component with JavaScript execution enabled. This design decision created a significant attack surface that allowed malicious actors to exploit the email client through crafted HTML content. The vulnerability stems from the improper handling of HTML email messages that contain embedded JavaScript code, which was executed directly within the email viewer without adequate sanitization or security controls.
The technical implementation of this vulnerability involves the QWebEngine component, which is a web rendering engine used by KDE applications for displaying HTML content. When KMail processed HTML emails, it leveraged this web engine to render messages, but failed to properly filter or sanitize JavaScript code embedded within the HTML. This behavior directly violates security principles of input validation and secure rendering, creating an environment where malicious JavaScript could execute with the privileges of the email client itself. The vulnerability is classified under CWE-79 as Cross-Site Scripting, specifically in the context of HTML email rendering, where client-side code execution occurs without proper sanitization of user-provided content.
The operational impact of CVE-2016-7968 extends beyond simple script execution, as it enables potential exploitation through various attack vectors including phishing campaigns, drive-by downloads, and social engineering attacks. An attacker could craft malicious HTML emails containing JavaScript that could perform actions such as stealing cookies, redirecting users to malicious sites, downloading additional malware, or even accessing the user's local system resources through browser APIs. The vulnerability is particularly dangerous because it operates at the application level within the email client, bypassing traditional network-level security controls and potentially allowing for privilege escalation or data exfiltration. This type of vulnerability aligns with ATT&CK technique T1203 - Exploitation for Client Execution, where adversaries leverage application vulnerabilities to execute malicious code on target systems.
The security implications of this vulnerability are further amplified by the widespread adoption of KMail within the KDE ecosystem and enterprise environments, where email clients often serve as primary attack vectors for initial compromise. Organizations using affected KMail versions were exposed to significant risk, as the vulnerability could be exploited through simple email delivery without requiring additional user interaction beyond opening the malicious message. Mitigation strategies included disabling JavaScript in the email viewer, updating to patched versions of KMail, and implementing email filtering solutions that could detect and block potentially malicious HTML content. The vulnerability highlighted the importance of secure web rendering in desktop applications and the need for comprehensive input validation when processing untrusted content, particularly in email clients that handle rich media content.