Microsoft's Patch Tuesday Fixes Two CVEs Under Active Attack

Microsoft's Patch Tuesday arrived with a sense of urgency this month, addressing two vulnerabilities under active attack and 66 other CVEs affecting Windows, Office, Office Services, Internet Explorer, Edge, Visual Studio, Web Apps, ChakraCore, Hyper-V Server, and Azure IoT SDK.

Of the 68 total CVEs addressed, 21 are rated as Critical, 45 are considered Important, and two are of Low severity. In addition to the two under active attack, two were listed as publicly known at the time of release, according to a report from Trend Micro's Zero-Day Initiative (ZDI).

The CVEs of highest priority are those under active attack. CVE-2018-8174, the more severe flaw, is a Windows VBScript Engine Remote Code Execution Vulnerability. The zero-day was detected and analyzed in April by Kaspersky Lab researchers, who reported it to Microsoft.

"This technique, until fixed, allowed criminals to force Internet Explorer to load, no matter which browser one normally used -- further increasing an already huge attack surface," says Anton Ivanov, security researcher at Kaspersky.

The zero-day bug is located in the VBScript Engine and its attacks are similar to those of browser vulnerabilities. It appears to be moving around as an Office document, likely Word, with an embedded Web page. These embedded pages are rendered by the VBScript Engine, says Dustin Childs, communications director for ZDI, so a user only has to visit an infected site for an attacker to execute code on their machine.

An attacker may also embed an ActiveX control marked "safe for initialization" in an Office doc or application that hosts the IE rendering engine. This appears to be the case here: Attackers send the file to targets; once it's opened, code execution occurs.

"This is a dangerous bug for a couple of reasons," Childs explains. "For users of IE, it acts like a standard browser bug - go to a bad website and get owned. However, VBScript Engine bugs have a broader impact since it also touches ActiveX controls and embedded Web pages in Office documents."

The other bug under active attack is CVE-2018-8120, a Win32k Elevation of Privilege Vulnerability affecting Windows 7, Server 2008, and Server 2008 R2. This bug lets an attacker who is logged onto a system run a specially crafted file to gain privileged access. While it's being actively used in malware, researchers are unsure how far the malware has spread.

"At that point the attacker would have full permissions to install or remove programs, add users, view, change, or delete data. This type of vulnerability is how a threat actor would elevate their privileges to gain full access to a system they have gained access to," says Chris Goettl, director of product management for security at Ivanti.

Microsoft issued 17 Critical, and 7 Important, patches for browser bugs. There are several patches issued for Office; the most important are those for Outlook and Sharepoint, ZDI reports. An Exchange update prevents a command injection attack, and the .NET Framework has a couple of patches rated Important.

Gren Wiseman, senior security researcher at Rapid7, points to one vulnerability, CVE-2018-8897 as "a nice example of coordinated disclosure" from OS vendors and the result of nearly all vendors incorrectly addressing debug exceptions stemming from Intel architecture chips. Microsoft, Apple, VMware FreeBSD, and multiple Linux distributions all posted advisories today.

For Microsoft Windows, CVE-2018-8897 could let a local attacker escalate privilege and run arbitrary code in kernel mode, he explains.

Microsoft this month also announced two public disclosures, meaning a vulnerability has been found and there is enough information on how it works to give an attacker the advantage before companies can update. One of these is CVE-2018-8141, a Windows kernel flaw; the other is CVE-2018-8170, a Windows Image bug that could lead to Elevation of Privilege. For both of these, an attacker could need to log on or obtain local access to exploit.