CVE-2016-7256 in Windows
Summary
by MITRE
atmfd.dll in the Windows font library in Microsoft Windows Vista SP2, Windows Server 2008 SP2 and R2 SP1, Windows 7 SP1, Windows 8.1, Windows Server 2012 Gold and R2, Windows RT 8.1, Windows 10 Gold, 1511, and 1607, and Windows Server 2016 allows remote attackers to execute arbitrary code via a crafted web site, aka "Open Type Font Remote Code Execution Vulnerability."
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Analysis
by VulDB Data Team • 09/09/2024
The vulnerability identified as CVE-2016-7256 represents a critical remote code execution flaw within the Windows font handling subsystem, specifically within the atmfd.dll component of the Windows font library. This vulnerability affects a broad range of Microsoft Windows operating systems including Vista SP2 through Windows 10 version 1607, as well as various server editions. The flaw manifests when the system processes specially crafted Open Type font files through web browsers or other applications that utilize the Windows font rendering engine, creating a dangerous attack vector that can be exploited remotely.
The technical root cause of this vulnerability lies in improper input validation within the atmfd.dll library, which is responsible for processing font files in the Open Type format. When a maliciously crafted font file is loaded, the library fails to properly validate the font structure and data, allowing attackers to manipulate memory layout and execute arbitrary code with the privileges of the affected application. This type of vulnerability is classified as a buffer overflow or memory corruption issue, specifically falling under CWE-121 which describes "Stack-based Buffer Overflow" and CWE-125 which addresses "Out-of-bounds Read" conditions. The vulnerability can be triggered through web browsers when they render web pages containing embedded malicious font files, making it particularly dangerous in the context of modern web browsing.
The operational impact of CVE-2016-7256 is severe and far-reaching, as it enables attackers to achieve complete system compromise without requiring any user interaction beyond visiting a malicious website. This vulnerability can be exploited in the context of the attacker's target's browsing session, potentially leading to full system takeover, data exfiltration, and persistence mechanisms. The attack surface is extensive given that the vulnerability affects multiple Windows versions and can be triggered through various vectors including web browsers, email clients, and other applications that render fonts. According to ATT&CK framework, this vulnerability maps to T1059.007 for "Command and Scripting Interpreter: JavaScript" and T1203 for "Exploitation for Client Execution" when exploited through web-based attacks, demonstrating the multi-layered nature of the threat.
The exploitation of this vulnerability typically involves crafting a malicious Open Type font file that contains specially designed structures to trigger the memory corruption in atmfd.dll. Attackers can deliver this payload through malicious websites, phishing emails, or compromised web services, making it particularly dangerous for enterprise environments where users frequently browse the internet and access potentially untrusted content. The vulnerability is particularly concerning because it operates at the system level and can be exploited by attackers with minimal privileges required to access the target system, often leveraging the trust relationships that exist between applications and the underlying operating system. Organizations should implement immediate mitigations including disabling font rendering for untrusted content, applying security patches, and monitoring for suspicious font-related activities in their network traffic, as this vulnerability represents a significant risk to operational security and data protection.