CVE-2017-7141 in macOS
Summary
by MITRE
An issue was discovered in certain Apple products. macOS before 10.13 is affected. The issue involves the "Mail" component. It allows remote attackers to bypass an intended off value of the "Load remote content in messages" setting, and consequently discover an e-mail recipient's IP address, via an HTML email message.
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Analysis
by VulDB Data Team • 01/20/2021
The vulnerability CVE-2017-7141 represents a significant privacy and security flaw within Apple's Mail application affecting macOS versions prior to 10.13. This issue specifically targets the email client's handling of remote content loading mechanisms, creating an unexpected bypass of security controls that were designed to protect user privacy. The vulnerability exists in the core email rendering functionality where the application fails to properly respect user configuration settings regarding remote content retrieval.
The technical implementation of this flaw involves the Mail component's HTML email parser which incorrectly processes certain HTML elements within email messages. When an attacker crafts a malicious HTML email, the application's remote content loading mechanism can be circumvented through specific HTML tag constructions that force the client to fetch remote resources despite the user's explicit setting to disable such functionality. This bypass occurs at the application layer where the security policy enforcement fails to properly validate the HTML content against the user's configured security preferences.
From an operational perspective, this vulnerability enables remote attackers to perform passive reconnaissance by discovering the IP addresses of email recipients. The mechanism works by embedding HTML elements that trigger remote resource requests, and when these requests are processed, they reveal network information about the recipient's system. This creates a privacy breach where an attacker can map network connections and potentially identify recipient infrastructure, representing a significant concern for users who rely on email privacy for personal or business communications. The vulnerability aligns with CWE-200, which addresses information exposure, and specifically relates to improper control of information flow, where the application fails to properly control how information is exposed to external entities.
The attack vector involves sending a specially crafted HTML email message that exploits the Mail application's parsing behavior to trigger remote resource fetching. This technique falls under ATT&CK tactic T1059, specifically T1059.007 for HTML Files, where adversaries leverage HTML email content to execute malicious behaviors. The impact extends beyond simple IP address disclosure to potentially enable further reconnaissance activities, as the attacker can determine network topology and potentially identify other services running on the target system. This vulnerability demonstrates the importance of proper input validation and security policy enforcement in email client applications, particularly when handling remote content requests.
Mitigation strategies for this vulnerability require immediate system updates to macOS 10.13 or later versions where Apple has implemented proper security controls for remote content handling. Users should also consider adjusting their email client security settings to disable remote content loading entirely, even when using updated software. Network administrators should monitor for potential exploitation attempts and implement email filtering rules that detect and block suspicious HTML content patterns. The vulnerability highlights the critical need for proper security testing of email rendering components and demonstrates how seemingly minor implementation flaws can create significant privacy risks. Organizations should also implement security awareness training to educate users about the risks of opening HTML emails from untrusted sources, as this vulnerability can be exploited through social engineering campaigns that rely on user trust to execute successful attacks.