CVE-2016-7966 in KMail
Summary
by MITRE
Through a malicious URL that contained a quote character it was possible to inject HTML code in KMail's plaintext viewer. Due to the parser used on the URL it was not possible to include the equal sign (=) or a space into the injected HTML, which greatly reduces the available HTML functionality. Although it is possible to include an HTML comment indicator to hide content.
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Analysis
by VulDB Data Team • 10/12/2022
The vulnerability identified as CVE-2016-7966 represents a cross-site scripting weakness in KMail's plaintext viewer component that stems from inadequate input sanitization of URL parameters. This flaw resides in the email client's handling of maliciously crafted URLs that contain quote characters, enabling attackers to inject HTML code into the email rendering process. The vulnerability specifically affects KMail's plaintext viewer functionality, which processes URLs embedded within email content and displays them to users in a manner that does not properly escape or validate the URL parameters before rendering them as HTML content. The security issue manifests when the email client's URL parser processes maliciously constructed URLs, allowing HTML injection that could potentially compromise user security. This vulnerability falls under the CWE-79 category of Cross-Site Scripting, specifically representing a variant where HTML injection occurs through URL parameters rather than direct user input fields. The attack vector leverages the plaintext viewer's parsing behavior, where the client processes URLs without sufficient sanitization of special characters that could otherwise be used to construct more sophisticated HTML injection payloads. The technical implementation of this vulnerability demonstrates a classic input validation flaw where the application fails to properly sanitize user-provided data before incorporating it into the HTML rendering context.
The operational impact of CVE-2016-7966 extends beyond simple HTML injection, as it creates potential for more serious security consequences when attackers leverage the ability to include HTML comment indicators to hide malicious content. While the vulnerability's effectiveness is limited by the parser's restriction on including equal signs and spaces, which constrains the types of HTML attributes and tags that can be constructed, the ability to inject HTML comments provides attackers with a method to obfuscate their malicious payloads. This limitation reduces the overall exploitability but does not eliminate the security risk entirely, as HTML comments can still be used to hide script tags or other malicious constructs that might be executed by the browser. The restriction on certain characters like the equals sign and space significantly reduces the available attack surface, but attackers can still craft payloads using the available characters to create functional HTML injection vectors. The vulnerability's impact is particularly concerning in email environments where users might inadvertently click on malicious links or where phishing attacks could leverage this weakness to create more convincing deceptive content. From an ATT&CK framework perspective, this vulnerability maps to T1566.001 (Phishing: Spearphishing Attachment) and T1059.001 (Command and Scripting Interpreter: PowerShell) through potential exploitation paths that could lead to more sophisticated attacks.
Mitigation strategies for CVE-2016-7966 should focus on implementing comprehensive input validation and sanitization measures within KMail's plaintext viewer component. The most effective approach involves modifying the URL parsing logic to properly escape or remove special characters that could be used for HTML injection, particularly ensuring that quote characters are handled appropriately during URL processing. Security patches should implement strict validation of URL parameters before rendering them in HTML contexts, with particular attention to character encoding and escaping mechanisms. Organizations should consider implementing Content Security Policy (CSP) headers that restrict the execution of inline scripts and limit the sources from which content can be loaded, providing an additional layer of protection against HTML injection attacks. The vulnerability's remediation should also include updating the email client's URL handling code to properly sanitize all URL parameters and ensure that any HTML content derived from URL parsing is rendered in a secure context that prevents script execution. Regular security updates and patches should be prioritized to address similar vulnerabilities in email client applications, as this type of weakness often indicates broader issues with input validation and sanitization practices within the application's architecture. The fix should be implemented following secure coding practices that emphasize defense in depth, ensuring that multiple layers of protection are in place to prevent similar vulnerabilities from occurring in other components of the email client software.