CVE-2021-40465 in Windows
Summary
by MITRE • 10/13/2021
Windows Text Shaping Remote Code Execution Vulnerability
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Analysis
by VulDB Data Team • 10/15/2021
This vulnerability resides in the Windows Text Shaping Engine component which processes text rendering operations for various applications and system functions. The flaw manifests as a remote code execution vulnerability that can be exploited through specially crafted text input processed by the text shaping engine. The vulnerability affects multiple Windows versions including Windows 10, Windows Server 2016, and Windows Server 2019, making it particularly concerning for enterprise environments where these systems are prevalent. The text shaping engine is responsible for converting text into visual representations and handling complex typography operations including font rendering, text layout, and character shaping. This particular vulnerability stems from improper handling of memory operations during text processing, specifically when the engine encounters malformed or malicious text input that triggers buffer overflows or memory corruption conditions.
The technical nature of this vulnerability aligns with CWE-121, which describes stack-based buffer overflow conditions, and CWE-787, which addresses out-of-bounds write operations. Attackers can leverage this weakness by crafting malicious text content that, when processed by the vulnerable Windows Text Shaping Engine, causes memory corruption that can be exploited to execute arbitrary code. The attack typically requires the target system to process the malicious text input through applications that utilize the Windows Text Shaping Engine, such as web browsers, word processors, or email clients. The vulnerability can be triggered remotely through web content, email attachments, or other network-based text processing scenarios, making it particularly dangerous for attackers seeking to compromise systems without physical access. The execution context of the exploit often depends on the privilege level of the affected application, potentially allowing attackers to gain system-level privileges if successful.
The operational impact of this vulnerability extends beyond simple code execution, as it can enable attackers to establish persistent access to compromised systems and potentially escalate privileges to SYSTEM level. Organizations running affected Windows versions face significant risk from this vulnerability, particularly those with less frequent patching schedules or limited security monitoring capabilities. The remote exploitation capability means that attackers can target systems from outside the network perimeter, making traditional network-based defenses insufficient for protection. Security teams must consider the broad attack surface that text processing applications present, as this vulnerability can be exploited through multiple vectors including web browsers, document readers, and email clients. The potential for privilege escalation makes this vulnerability particularly attractive to threat actors, as it can provide a foundation for broader network compromise and data exfiltration operations.
Mitigation strategies should focus on immediate patch deployment from Microsoft, which addresses the underlying memory handling issues in the text shaping engine. Organizations should prioritize patching across all affected Windows versions, particularly those running in enterprise environments where the risk of exploitation is highest. Network segmentation and application whitelisting can provide additional defense-in-depth layers, limiting the potential impact of successful exploitation attempts. Security monitoring should include detection of unusual text processing activities and potential buffer overflow indicators within system logs. The vulnerability also highlights the importance of secure coding practices and input validation, as the flaw stems from inadequate memory management during text processing operations. Implementing exploit prevention technologies such as address space layout randomization and data execution prevention can further reduce the exploitability of similar vulnerabilities. Regular security assessments and penetration testing should include evaluation of text processing components to identify potential weaknesses in custom applications that may be susceptible to similar text shaping vulnerabilities.