CVE-2018-5731 in Heimdal Pro
Summary
by MITRE
An issue was discovered in Heimdal PRO 2.2.190. As part of the scanning feature, a process called md.hs writes an executable called CS1.tmp to C:\windows\TEMP. Afterwards the executable is run. It is possible for an attacker to create the file first, let md.hs overwrite it, and then rewrite the file in the window between md.hs closing the file and executing it. This can be exploited via opportunistic locks and a high priority thread. The vulnerablity is triggered when a scan starts. NOTE: any affected Heimdal products are completely unrelated to the Heimdal vendor of a Kerberos 5 product on the h5l.org web site.
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Analysis
by VulDB Data Team • 01/16/2020
The vulnerability identified as CVE-2018-5731 affects Heimdal PRO version 2.2.190 and represents a critical file system race condition that enables privilege escalation through malicious file replacement during antivirus scanning operations. This flaw resides within the md.hs process responsible for executing security scans, specifically targeting the temporary file creation and execution workflow in the Windows TEMP directory. The vulnerability stems from improper handling of temporary file operations where the system creates a file named CS1.tmp in the C:\windows\TEMP directory without adequate security controls to prevent malicious interference. The technical implementation involves a classic race condition scenario where an attacker can manipulate the file creation sequence to substitute a legitimate executable with a malicious payload before execution occurs.
The operational impact of this vulnerability extends beyond simple privilege escalation as it allows attackers to execute arbitrary code with elevated privileges, potentially compromising the entire system. The exploitation technique leverages opportunistic locks and high priority threading to create a window of opportunity between when the md.hs process closes the temporary file and when it executes the file. This timing attack requires precise coordination and demonstrates the dangerous implications of inadequate file system security measures in security software applications. The vulnerability specifically activates during the initiation of security scans, making it particularly dangerous as it can be triggered by routine system operations without requiring special user interaction or elevated privileges from the attacker's perspective.
Security practitioners should recognize this vulnerability as a direct implementation of CWE-367, which addresses Time-of-Check to Time-of-Use (TOCTOU) race conditions that occur when system resources are accessed at different times, creating opportunities for malicious manipulation. The attack vector aligns with ATT&CK technique T1059.001 for command and scripting interpreter, as successful exploitation would enable attackers to execute malicious code through the compromised scanning process. Mitigation strategies must include immediate patching of affected Heimdal PRO versions, implementation of proper file permissions for temporary directories, and deployment of process monitoring to detect unauthorized file creation in system temporary locations. Organizations should also consider implementing application whitelisting policies and restricting write access to critical system directories to prevent similar race condition vulnerabilities in other security applications. The vulnerability highlights the critical importance of secure coding practices in security software, particularly when handling temporary files and system resources, as these applications often operate with elevated privileges and represent prime targets for exploitation.