CVE-2017-8696 in Windows
Summary
by MITRE
Windows Uniscribe in Microsoft Windows Server 2008 SP2 and R2 SP1; Windows 7 SP1; Office 2007 SP3; Office 2010 SP2; Word Viewer; Office for Mac 2011 and 2016; Skype for Business 2016; Lync 2013 SP1; Lync 2010; Lync 2010 Attendee; and Live Meeting 2007 Add-in and Console allows an attacker to execute code remotely via a specially crafted website or a specially crafted document or email attachment, aka "Microsoft Graphics Component Remote Code Execution."
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Analysis
by VulDB Data Team • 01/12/2021
The vulnerability identified as CVE-2017-8696 represents a critical remote code execution flaw within Microsoft's Uniscribe text processing component that affects multiple Windows operating systems and Office products. This vulnerability resides in the Windows Uniscribe library responsible for complex text layout and rendering operations, particularly handling Unicode text processing and font rendering. The flaw manifests when the affected components process specially crafted text sequences that trigger buffer overflows or memory corruption conditions within the graphics rendering pipeline. Attackers can exploit this vulnerability by delivering malicious content through web pages, documents, or email attachments that contain crafted Unicode text sequences designed to trigger the vulnerable code path. The vulnerability is particularly dangerous because it can be exploited across multiple Microsoft products and platforms, including legacy systems like Windows Server 2008 and Office 2007, making it a widespread concern for enterprise environments.
The technical exploitation of CVE-2017-8696 leverages the interaction between Uniscribe's text processing capabilities and Microsoft's graphics rendering engine, specifically through the handling of complex text shaping operations. When a user opens a malicious document or visits a compromised website containing crafted text elements, the Uniscribe component processes these inputs and triggers memory corruption through improper bounds checking or buffer overflow conditions. This vulnerability maps to CWE-121, which describes stack-based buffer overflow conditions, and CWE-125, which covers out-of-bounds read conditions that can lead to arbitrary code execution. The attack vector typically involves embedding malicious Unicode text sequences within Office documents or HTML content that when rendered by the vulnerable components, causes the execution flow to be hijacked. The exploitation process often requires the attacker to carefully craft input that will cause the Uniscribe engine to allocate insufficient memory for text processing operations, leading to memory corruption that can be leveraged for code execution.
The operational impact of this vulnerability extends beyond simple remote code execution to encompass significant security risks for organizations relying on affected Microsoft products. Attackers can leverage this vulnerability to gain full system control without requiring user interaction beyond opening a malicious document or visiting a compromised website, making it particularly dangerous for enterprise environments where users frequently open documents from external sources. The vulnerability affects a broad range of Microsoft products including Office 2007 through Office 2016, Office for Mac 2011 and 2016, and various Microsoft communication products, creating extensive attack surface. Organizations using these vulnerable components face risks of data breaches, system compromise, and potential lateral movement within networks. The vulnerability also aligns with ATT&CK technique T1203, which describes exploitation of remote services and T1059, covering command and scripting interpreter usage, as successful exploitation typically enables attackers to establish persistent access and execute additional malicious payloads.
Mitigation strategies for CVE-2017-8696 should focus on immediate patch deployment and operational security measures to protect against exploitation attempts. Microsoft released security updates addressing this vulnerability through regular security bulletins, and organizations should prioritize applying these patches across all affected systems. Network-based mitigations include implementing web application firewalls, content filtering solutions, and email security controls that can detect and block malicious documents containing crafted Unicode text sequences. Organizations should also consider implementing principle of least privilege controls, restricting user permissions, and deploying sandboxing solutions for document processing. Security monitoring should focus on detecting unusual document opening patterns, web browsing behavior, and network connections to suspicious domains. The vulnerability demonstrates the importance of maintaining up-to-date security patches and highlights the risks associated with supporting legacy systems, as many of the affected products have reached end-of-life status, making patching more challenging for organizations. Regular security assessments and vulnerability scanning should be conducted to identify systems that may still be running vulnerable components and require additional protective measures.