CVE-2018-0595 in Skype
Summary
by MITRE
Untrusted search path vulnerability in the installer of Skype for Windows allows an attacker to gain privileges via a Trojan horse DLL in an unspecified directory.
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Analysis
by VulDB Data Team • 02/22/2020
The vulnerability identified as CVE-2018-0595 represents a critical untrusted search path weakness within the Windows installer component of Skype software. This flaw stems from the installer's improper handling of dynamic link library loading sequences, creating an exploitable condition where malicious actors can insert unauthorized code into the system execution flow. The vulnerability specifically affects the installation process of Skype for Windows, where the installer fails to properly validate or sanitize the search paths used when loading required libraries. This design oversight allows attackers to place malicious DLL files in directories that the installer searches before checking legitimate system locations, effectively enabling code injection during the installation process.
The technical exploitation of this vulnerability occurs through a Trojan horse DLL attack vector that leverages the installer's trust in specific directory paths. When Skype's installer executes, it follows a predetermined search order that includes user-writable directories, potentially allowing an attacker to place a malicious DLL with the same name as a legitimate library. This creates a privilege escalation scenario where the malicious code executes with the elevated privileges of the installer process, typically running with system-level permissions. The vulnerability falls under CWE-427 Uncontrolled Search Path Element, which specifically addresses the issue of applications using search paths that include untrusted directories, making it susceptible to path manipulation attacks.
The operational impact of CVE-2018-0595 extends beyond simple privilege escalation to encompass broader system compromise capabilities. Attackers can leverage this vulnerability to execute arbitrary code with elevated privileges, potentially leading to full system compromise, data exfiltration, or persistence mechanisms. The attack requires minimal user interaction since the vulnerability is triggered during the normal installation process, making it particularly dangerous in enterprise environments where software deployment occurs regularly. The vulnerability's exploitation aligns with ATT&CK technique T1068, which covers privilege escalation through local exploits, and T1574, which addresses hijacking execution flows through dynamic link library loading. Organizations using Skype in their deployment pipelines face significant risk, as this vulnerability can be exploited by adversaries to gain unauthorized access to systems during routine software updates or installations.
Mitigation strategies for CVE-2018-0595 should focus on both immediate remediation and long-term architectural improvements. Microsoft and Skype developers addressed this vulnerability through patches that modified the installer's library loading behavior to prioritize system directories and implement proper path validation. Organizations should ensure immediate patch deployment and implement additional safeguards such as restricting write permissions to directories used by installation processes, monitoring for unauthorized DLL placements, and employing application whitelisting solutions. The vulnerability highlights the importance of secure coding practices and proper input validation, particularly in installation and update mechanisms. Security teams should also consider implementing network monitoring to detect unusual DLL loading patterns and establish robust software supply chain security measures to prevent malicious code injection at any point in the installation lifecycle.