CVE-2016-7967 in KMail
Summary
by MITRE
KMail since version 5.3.0 used a QWebEngine based viewer that had JavaScript enabled. Since the generated html is executed in the local file security context by default access to remote and local URLs was enabled.
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Analysis
by VulDB Data Team • 10/12/2022
The vulnerability identified as CVE-2016-7967 represents a critical security flaw in KMail email client versions 5.3.0 and later that utilized the QWebEngine based viewer component. This flaw emerged from the default configuration of the web engine component which enabled JavaScript execution within the local file security context. The vulnerability stems from the improper handling of HTML content generated by email messages, creating an environment where maliciously crafted emails could exploit the web engine's security model to gain unauthorized access to local system resources.
The technical implementation of this vulnerability involves the QWebEngineView component within KDE's email client architecture, which was designed to render HTML emails with full web capabilities including JavaScript execution. When KMail processed HTML email content, it leveraged the QWebEngine's default security policies that allowed scripts to access both local and remote resources without proper sandboxing. This configuration created a path where JavaScript code within malicious emails could potentially access local files, execute arbitrary commands, or establish connections to remote servers. The vulnerability specifically exploited the fact that the web engine's default security context did not properly restrict file system access, allowing local file protocol handlers to be invoked from within the rendered HTML content.
The operational impact of this vulnerability extends beyond simple privilege escalation as it enabled attackers to craft emails that could compromise user systems through various attack vectors. An attacker could embed malicious JavaScript code within HTML emails that would execute when the user opened the message, potentially leading to unauthorized file access, system reconnaissance, or even remote code execution depending on the target system configuration. The vulnerability particularly affected users who regularly opened HTML emails from untrusted sources, as the malicious payload could be triggered simply by viewing the email content. This represents a classic cross-site scripting attack vector that was exacerbated by the web engine's permissive security model.
Mitigation strategies for this vulnerability required immediate patching of affected KMail versions to disable JavaScript execution or properly configure the QWebEngine security context to prevent local file access. System administrators should have implemented email filtering policies to block HTML emails from untrusted sources and configured user permissions to limit file system access. The vulnerability aligns with CWE-79 which describes cross-site scripting flaws, and maps to ATT&CK technique T1059.007 for script execution. Organizations should have deployed email security solutions that could analyze and sanitize HTML content before delivery, while users needed to be educated about the risks of opening HTML emails from unknown senders. The fix involved modifying the web engine's security policies to enforce proper sandboxing and restrict local file access for rendered content, ensuring that even if JavaScript was enabled, it could not access system resources beyond the intended scope of the email viewer functionality.