CVE-2021-24077 in Windows
Summary
by MITRE • 02/26/2021
Windows Fax Service Remote Code Execution Vulnerability This CVE ID is unique from CVE-2021-1722.
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 02/26/2021
The Windows Fax Service remote code execution vulnerability represents a critical security flaw that allows attackers to execute arbitrary code on affected systems without authentication. This vulnerability specifically impacts the fax service component of Microsoft Windows operating systems, which provides fax capabilities for sending and receiving faxes through network connections. The flaw exists within the service's handling of incoming fax data and processing mechanisms, creating an exploitable condition that can be leveraged by remote attackers to gain unauthorized system access.
The technical implementation of this vulnerability stems from improper input validation and memory handling within the fax service daemon process. When the service processes incoming fax data or handles specific fax-related commands, it fails to properly validate user-supplied inputs, leading to potential buffer overflow conditions or other memory corruption scenarios. This flaw aligns with common weakness types documented in CWE-121, which describes heap-based buffer overflow conditions, and CWE-787, which covers out-of-bounds write operations. Attackers can craft malicious fax data or commands that trigger the vulnerable code paths, potentially resulting in arbitrary code execution with system-level privileges.
The operational impact of this vulnerability extends beyond simple remote code execution, as it enables attackers to establish persistent access to compromised systems while maintaining stealth and operational control. The fax service typically runs with elevated privileges and has network exposure through standard fax protocols, making it an attractive target for adversaries seeking to maintain long-term access. This vulnerability can be leveraged in conjunction with other attack techniques to create comprehensive compromise scenarios, aligning with ATT&CK technique T1059.007 for command and script interpreter execution and T1068 for exploit for privilege escalation.
Security professionals should recognize that this vulnerability presents a significant risk to organizations relying on fax services or systems that have the Windows Fax Service component installed. The attack surface is particularly concerning because fax services often run continuously in enterprise environments, providing persistent network endpoints that attackers can target. Organizations should implement immediate mitigations including disabling unnecessary fax service components, applying security patches from Microsoft, and implementing network segmentation controls to limit lateral movement potential.
The exploitation of this vulnerability typically requires minimal privileges and can be automated through various attack frameworks, making it particularly dangerous in environments where fax services are enabled but not properly monitored or secured. Network monitoring solutions should be configured to detect unusual fax-related traffic patterns that might indicate exploitation attempts, while endpoint detection and response systems should be tuned to identify suspicious process creation patterns associated with the fax service component. System administrators should also review existing access controls and ensure that only authorized personnel have administrative access to fax service configurations and related components.
Organizations should prioritize patch management processes to address this vulnerability promptly, as Microsoft has released security updates specifically targeting the Windows Fax Service remote code execution flaw. The vulnerability demonstrates the importance of maintaining comprehensive inventory control over all system services and ensuring that unnecessary components are disabled or removed from production systems. Security teams should also conduct thorough risk assessments to identify all systems running fax services and evaluate their exposure to this particular threat vector while implementing appropriate defensive measures against potential exploitation attempts.