Microsoft Issues 9 Critical Security Patches

Today is the second Tuesday of the month, and Microsoft is right on schedule with 59 security fixes, nine of which are considered Critical in severity.

None of the vulnerablities were previously known or exploited, and 49 are ranked Important and one as Moderate. 

The latest release affects Windows, Internet Explorer, Edge, ChakraCore, Microsoft Office and Office Services and Web Apps, Microsoft Dynamics 365, SQL Server Management Studio, Windows Update Assistant, and Open Source Software. It's a smaller-volume roundup compared with many Patch Tuesdays of late: September's fixed 80 bugs and August's patched 93, including a wormable remote code execution (RCE) flaw. In July, Microsoft addressed 77 vulnerabilities.

October continued the trend of patching remote desktop vulnerabilities, which have been common the past four months. CVE-2019-1333 is an RCE flaw that exists in the Remote Desktop Client when a user connects with a malicious server. An attacker who successfully exploited the bug could view, change, or delete data; install programs; or create new accounts with user rights.

To exploit CVE-2019-1333, an attacker would need to control a server and convince a target to connect using a social engineering scam, DNS poisoning, or a man-in-the-middle attack. They could also compromise a legitimate server, host malicious code on it, and wait for someone to connect to it. Today's patch corrects how Remote Desktop Client handles connection requests.

While this RCE vulnerability is only being disclosed today and attackers haven't yet taken advantage of it, Microsoft warns exploitation is more likely for this one. The patch should be applied "immediately," says Richard Melick, senior technical product manager at Automox, even though this bug isn't as severe as the remote desktop flaws disclosed back in August.

"Lateral access through a network only requires one compromised machine and with this capability in the hands of an attacker, their actions would be masked longer due to the escalated access," Melick says of the implications of this vulnerability in the wrong hands. Even so, the requirement for attackers to convince a target to connect makes this tough to exploit.

Important-ranked patch CVE-2019-1326 is a Remote Desktop Protocol denial-of-service bug that exists when an attacker connects to the target system using RDP and sends specially crafted requests. If successful, they could cause the RDP service on a target system to stop responding.

Microsoft also re-released CVE-2019-1367, which was first deployed on Sept. 23 as an out-of-band patch to address a scripting engine memory corruption vulnerability in Internet Explorer that was under active attack. The bug could let an attacker execute arbitrary code at the same privilege level as a legitimate user and in doing so, install programs, view and change data, and create new accounts with full user rights while the legitimate user is logged in as an admin.

The update to this patch released today addresses a known printing issue some users might have experienced after installing any of the Security Updates, IE Cumulative Updates, or Monthly Rollups released on Sept. 23 or Oct. 3 for Internet Explorer 9, 10, or 11, or Windows.

For those who use the Azure App Service, another RCE vulnerability worth noting is CVE-2019-1372. This exists when Azure App Service/Antares on the Azure Stack fails to check the length of a buffer before copying the memory to it. An attacker who successfully exploited this could allow an unprivileged function run by the user to execute code in the context of NT Authority system and escape the sandbox. The patch ensures Azure App Services sanitizes user inputs.

"If you have the Azure App Service deployed to your Azure Stack, this patch should be prioritized," says Qualys director of product management Jimmy Graham.

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