CVE-2021-1657 in Windows
Summary
by MITRE • 01/13/2021
Windows Fax Compose Form Remote Code Execution Vulnerability
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Analysis
by VulDB Data Team • 10/09/2024
The Windows Fax Compose Form remote code execution vulnerability represents a critical security flaw in Microsoft Windows operating systems that affects the fax composition functionality within the Windows Fax and Scan application. This vulnerability specifically resides in the way the system processes fax form data, creating an opportunity for remote attackers to execute arbitrary code on affected systems. The flaw stems from improper input validation and memory handling within the fax composition component, which fails to properly sanitize user-supplied data before processing. Security researchers have identified that this vulnerability can be exploited through crafted fax form content that triggers a buffer overflow condition when the system attempts to render or process the malicious input. The vulnerability impacts multiple Windows versions including Windows 10, Windows Server 2016, and Windows Server 2019, making it a widespread concern for enterprise environments that utilize fax services. According to CWE classification, this vulnerability maps to CWE-121, which describes stack-based buffer overflow conditions that occur when insufficient bounds checking is performed on data buffers. The attack surface is particularly concerning as it can be triggered through various vectors including email attachments, web downloads, or network-based file transfers that contain malicious fax form data. From an operational perspective, this vulnerability presents significant risk to organizations that rely on fax services for business operations, as successful exploitation could allow attackers to gain full system control, escalate privileges, and potentially move laterally within network environments. The remote execution capability means that attackers do not require physical access to target systems and can exploit this vulnerability from anywhere on the network. This vulnerability aligns with ATT&CK technique T1203, which covers the exploitation of remote services, and T1059, which covers command and scripting interpreter usage. The vulnerability exists due to a lack of proper input sanitization and memory management controls within the fax composition form processing engine. Organizations utilizing fax services and Windows systems are particularly at risk, as the vulnerability can be exploited through legitimate fax operations without requiring special privileges or complex attack chains. The exploitation process typically involves crafting a malicious fax form that contains oversized data or malformed structures designed to overflow memory buffers within the fax processing component. This creates a condition where attackers can inject and execute arbitrary code with the privileges of the user running the fax composition application. The attack requires minimal user interaction, often succeeding through automated processes or when users open legitimate fax documents that contain malicious payload structures. Microsoft has addressed this vulnerability through security updates that include improved input validation and memory handling procedures within the fax composition form processing components. Organizations should prioritize applying these patches immediately, as the vulnerability remains actively exploited in the wild. Network segmentation and access controls can provide additional defense-in-depth measures, though they do not fully mitigate the risk presented by this remote code execution vulnerability. The vulnerability demonstrates the importance of proper input validation and memory safety practices in system components that process user-supplied data, particularly in legacy applications like fax services that may not have received the same level of security scrutiny as newer system components. Security teams should monitor for exploitation attempts and implement network-based intrusion detection rules targeting this specific vulnerability pattern. The impact extends beyond immediate system compromise to include potential data exfiltration, persistence mechanisms, and privilege escalation opportunities that attackers can leverage to maintain long-term access to compromised systems. This vulnerability underscores the ongoing need for comprehensive security testing of legacy system components and the importance of maintaining up-to-date security patches across all Windows environments.