CVE-2020-0787 in Windows
Summary
by MITRE
An elevation of privilege vulnerability exists when the Windows Background Intelligent Transfer Service (BITS) improperly handles symbolic links, aka 'Windows Background Intelligent Transfer Service Elevation of Privilege Vulnerability'.
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Analysis
by VulDB Data Team • 09/09/2024
The vulnerability identified as CVE-2020-0787 represents a critical elevation of privilege flaw within the Windows Background Intelligent Transfer Service (BITS) component. This service operates as a core Windows functionality responsible for managing background file transfers between applications and servers, making it a critical system component that requires robust security controls. The vulnerability specifically arises from BITS' improper handling of symbolic links, which creates a pathway for malicious actors to escalate their privileges within the Windows operating system. The flaw exists in the way BITS processes symbolic link references during file transfer operations, allowing unauthorized users to manipulate file paths and potentially execute code with elevated privileges.
From a technical perspective, the vulnerability stems from insufficient validation of symbolic link targets within the BITS service execution context. When BITS processes file transfers, it may encounter symbolic links that point to sensitive system locations or files that should not be accessible through normal user operations. The service fails to properly resolve these symbolic links or validate their targets against the security boundaries that normally protect system resources. This improper handling creates a condition where an attacker can craft malicious symbolic links that, when processed by BITS, result in unintended file system access or execution privileges. The vulnerability aligns with CWE-59, which specifically addresses improper handling of symbolic links, and demonstrates how such flaws can be exploited to gain unauthorized access to system resources.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it provides attackers with a method to bypass standard Windows security mechanisms including User Account Control and file system permissions. An attacker who can successfully exploit this vulnerability can potentially gain SYSTEM-level privileges, allowing them to modify critical system files, install malicious software, or establish persistent access to the compromised system. The attack surface is particularly concerning because BITS runs with elevated privileges and is frequently used by legitimate applications, making the exploitation vector accessible through normal system operations. This vulnerability can be particularly dangerous in enterprise environments where BITS is commonly used for software updates, patch management, and other administrative functions.
Security professionals should implement multiple layers of mitigation to address this vulnerability effectively. Immediate remediation involves applying the Microsoft security update released in June 2020, which patches the symbolic link handling behavior within BITS. Organizations should also consider implementing additional controls such as monitoring for suspicious symbolic link creation patterns and restricting unnecessary file system access for BITS operations. The vulnerability demonstrates characteristics consistent with ATT&CK technique T1068, which involves local privilege escalation through Windows service manipulation. Network administrators should monitor for unusual BITS activity patterns and implement appropriate access controls to limit the potential impact of such exploits. The remediation process should include comprehensive testing to ensure that legitimate BITS functionality remains intact while addressing the privilege escalation vector. Organizations should also review their overall security posture and implement principle of least privilege controls to minimize the potential damage from any successful exploitation attempts.