Massive Skype Zero-Day Enables Remote Crashes

A critical vulnerability in Skype for Web could allow attackers to remotely execute code and crash systems. Microsoft has fixed the flaw, which remains a threat to anyone who has not updated their software.

Vulnerability Lab security researcher Benjamin Kunz Mejri discovered the zero-day vulnerability during a team conference call. It affects Skype versions 7.2, 7.35, and 7.36, and is considered a high-security risk with a 7.2 CVSS score.

Researchers state the stack buffer overflow flaw, CVE-2017-9948, has a "critical impact" to local and remote Skype users. Attackers can crash the software with a request to overwrite the register of the active software process. This lets them execute their own malicious code on affected and connected systems via Skype.

"The limitation of the transmitted size and count for images via print of the remote session clipboard has not secure limitation or restriction," Vulnerability Lab states. "Attackers are able to crash the software with one request to overwrite the eip register of the active software process."

This flaw affects the 'MSFTEDIT.DLL' dynamic link library of the Windows 8 (x86) operating system, researchers explain, and it is located in the "clipboard format" function of the Skype software. Attackers need only a low-privilege Skype account to launch a successful attack and do not need to interact with victims.

The vulnerability was reported to Microsoft's Security Response Center on May 16, and Microsoft issued a patch for the problem in Skype version 7.37 on June 8. Users are urged to update their software to avoid cyberattacks.