CVE-2021-42276 in Windows
Summary
by MITRE • 11/10/2021
Microsoft Windows Media Foundation Remote Code Execution Vulnerability
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Analysis
by VulDB Data Team • 11/12/2021
Microsoft Windows Media Foundation contains a remote code execution vulnerability that arises from improper handling of specially crafted media files during parsing operations. This flaw exists in the way the media foundation component processes certain multimedia content, particularly within the handling of specific codec structures and metadata fields. The vulnerability stems from a lack of proper input validation and bounds checking when processing malformed media files, creating opportunities for attackers to execute arbitrary code on affected systems. The issue affects multiple Windows versions including Windows 10, Windows 11, Windows Server 2016, and Windows Server 2019, making it a widespread concern across enterprise environments. According to CWE-129, this vulnerability represents an insufficient validation of length of input data, which directly enables buffer over-read conditions during media file processing. The attack surface expands significantly when considering that media files can be delivered through various vectors including email attachments, web downloads, and malicious websites that leverage the Windows Media Foundation component for automatic playback. This vulnerability aligns with ATT&CK technique T1203 by enabling initial access through malicious media files and T1059 by allowing execution of commands through compromised media processing pipelines. The remote code execution capability allows attackers to gain full system control, potentially leading to data exfiltration, persistence mechanisms, and lateral movement within networks. Exploitation typically requires the victim to open or play a specially crafted media file, making social engineering components essential for successful attacks. The vulnerability's impact is particularly severe in enterprise environments where users may automatically play media content from untrusted sources, and where the Media Foundation component is frequently invoked during routine operations. Organizations using Microsoft Edge, Internet Explorer, or any application that relies on Windows Media Foundation for media processing are at risk, as the component operates at a system level rather than within isolated application contexts. The flaw demonstrates how multimedia processing components can serve as attack vectors in modern operating systems, highlighting the importance of secure coding practices and proper input validation in system-level components. This vulnerability exemplifies the challenges of securing multimedia frameworks where complex codec parsing and processing operations must balance performance with security considerations.
The technical exploitation of this vulnerability occurs when a malicious media file triggers improper memory handling within the Windows Media Foundation parser. The component fails to properly validate the size and structure of media file headers, allowing attackers to craft payloads that cause buffer overflows or memory corruption during parsing operations. This type of vulnerability commonly maps to CWE-121, which describes the condition where insufficient bounds checking leads to buffer overflow conditions, and CWE-125, which addresses out-of-bounds read errors that can result in information disclosure or code execution. The attack requires minimal user interaction beyond opening or playing the malicious media file, making it particularly dangerous for phishing campaigns and targeted attacks. Security researchers have identified that the vulnerability can be triggered through various media formats including but not limited to mp4, wmv, and mpeg files, though the specific triggering conditions depend on the exact codec structures used in the malicious payload. The exploitation process typically involves crafting a media file with malformed headers that cause the Media Foundation component to read beyond allocated memory boundaries, potentially leading to controlled code execution. Attackers can leverage this vulnerability to deploy malware, establish persistent backdoors, or perform privilege escalation attacks depending on the execution context and target system configuration. The vulnerability's severity classification as critical reflects the ease of exploitation and the potential for full system compromise without requiring user interaction beyond basic media playback operations. Organizations should note that this vulnerability affects not just individual user systems but also server environments where media processing occurs, including web servers, content delivery networks, and media streaming platforms.
Mitigation strategies for CVE-2021-42276 should focus on immediate patch management and operational security improvements. Microsoft released security updates that address the vulnerability through proper input validation and bounds checking in the Media Foundation component, requiring administrators to deploy these patches promptly across all affected systems. Organizations should implement network segmentation and content filtering to prevent automatic playback of potentially malicious media files, particularly in environments where users may encounter untrusted content. The principle of least privilege should be enforced to limit the impact of successful exploitation, ensuring that media processing operations run with minimal required permissions. Security monitoring should include detection of unusual media file processing activities and anomalous network traffic patterns associated with media content delivery. Additionally, organizations should consider disabling automatic media playback in web browsers and email clients, and implement application whitelisting policies to restrict which media applications can be executed on systems. The vulnerability highlights the importance of secure coding practices in system-level components and underscores the need for regular security assessments of multimedia frameworks. Network administrators should monitor for suspicious file transfers and implement email filtering solutions that can identify and block potentially malicious media attachments. The implementation of security awareness training for users can help reduce the risk of successful exploitation through social engineering campaigns that rely on media file delivery. Organizations should also consider deploying endpoint detection and response solutions that can identify exploitation attempts targeting the Media Foundation component and provide real-time alerting capabilities. Proper incident response procedures should include specific guidance for handling potential exploitation of this vulnerability, including system isolation, forensic analysis, and remediation steps to ensure complete removal of any potential backdoors or malicious payloads that may have been deployed.