Quantum Secular Labs / Blog / Advisories

CVE-2017-6517: Microsoft Skype: Authentication bypass

CVE-2017-6517 is rated critical with a CVSS v3.0 base score of 9.8 and affects Microsoft Skype. Per its scoring, it can be exploited over the network, without authentication, without any user interaction. The scored impact on confidentiality, integrity and availability is the highest available.

Vulnerability description

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.

Severity breakdown

CVSS v3.0 9.8: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Attack vector: Network. Exploitable remotely over the network, with no need for local or physical access.
Attack complexity: Low. No special conditions; the attack can be repeated reliably.
Privileges required: None. No account or prior access is needed.
User interaction: None. No action from any user is needed.
Scope: Unchanged. Impact stays within the vulnerable component.
Confidentiality impact: High. Total loss of confidentiality; sensitive data can be fully disclosed.
Integrity impact: High. Total loss of integrity; data or system state can be fully modified.
Availability impact: High. Total loss of availability; the component can be shut down.

Underlying weakness

CWE-427: Uncontrolled Search Path Element

The product uses a fixed or controlled search path to find resources, but one or more locations in that path can be under the control of unintended actors.

Affected products

Microsoft Skype: 7.16.0.102