CVE-2017-6517 in Skype
Summary
by MITRE
Microsoft Skype 7.16.0.102 contains a vulnerability that could allow an unauthenticated, remote attacker to execute arbitrary code on the targeted system. This vulnerability exists due to the way .dll files are loaded by Skype. It allows an attacker to load a .dll of the attacker's choosing that could execute arbitrary code without the user's knowledge.The specific flaw exists within the handling of DLL (api-ms-win-core-winrt-string-l1-1-0.dll) loading by the Skype.exe process.
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Analysis
by VulDB Data Team • 11/15/2022
The vulnerability identified as CVE-2017-6517 represents a critical remote code execution flaw in Microsoft Skype version 7.16.0.102 that exposes systems to unauthorized remote exploitation. This vulnerability operates through a dangerous dynamic link library loading mechanism that fundamentally compromises the application's security model. The flaw specifically resides in how Skype.exe processes the loading of Windows runtime string libraries, creating an attack vector that enables remote code execution without user interaction or authentication. The vulnerability's impact extends beyond simple privilege escalation as it provides attackers with complete system compromise capabilities through the manipulation of legitimate system loading processes.
The technical root cause of this vulnerability stems from improper DLL loading practices within the Skype application architecture, which aligns with CWE-427 Uncontrolled Search Path Element and CWE-74 Improper Neutralization of Special Elements in Output Used by a Downstream Component. The flaw manifests when Skype.exe attempts to load the api-ms-win-core-winrt-string-l1-1-0.dll file, creating an opportunity for attackers to manipulate the system's dynamic loading sequence. This vulnerability operates at the operating system level, leveraging Windows' DLL search order mechanism to load malicious code instead of legitimate system components. The attack vector is particularly dangerous because it requires no user interaction or authentication, making it an ideal candidate for automated exploitation campaigns. The vulnerability exists within the application's dynamic loading behavior rather than through traditional input validation flaws, which makes it more difficult to detect through standard security scanning methods.
The operational impact of CVE-2017-6517 is severe and multifaceted, as it provides attackers with complete system compromise capabilities without requiring any user interaction. This vulnerability allows remote attackers to execute arbitrary code with the privileges of the Skype process, which typically runs with elevated permissions on modern Windows systems. The attack scenario enables threat actors to deploy malware, establish backdoors, or perform data exfiltration directly from compromised systems. From an adversary perspective, this vulnerability maps directly to ATT&CK technique T1059 Command and Scripting Interpreter, as it allows for arbitrary code execution through legitimate system processes. The vulnerability's exploitation does not require any special user privileges or complex attack chains, making it particularly attractive for automated exploitation tools and botnets. Once exploited, attackers can maintain persistent access to the compromised system while remaining undetected by typical user-level security controls.
Mitigation strategies for CVE-2017-6517 must address both the immediate vulnerability and broader security posture issues. Organizations should implement immediate patch management procedures to upgrade to Skype versions that resolve this vulnerability, as Microsoft released security updates to address the specific DLL loading flaw. System administrators should also consider implementing application control policies that restrict the loading of unauthorized DLL files, particularly in enterprise environments. The vulnerability's nature suggests that implementing DEP (Data Execution Prevention) and ASLR (Address Space Layout Randomization) should be verified as active protections within the Skype process execution environment. Network-level mitigations could include blocking Skype's communication ports and implementing firewall rules that prevent unauthorized DLL loading attempts. Additionally, monitoring for unusual DLL loading patterns and implementing behavioral analysis tools can help detect exploitation attempts before they succeed. Security teams should also consider implementing endpoint detection and response solutions that can identify the specific DLL loading sequences associated with this vulnerability, as this represents a classic attack pattern that can be detected through process monitoring and file system activity analysis.