This week, patch Tuesday saw updates issued to address actively exploited security vulnerabilities in Internet Explorer, along with a swathe of fixes for a number of other critical Microsoft security vulnerabilities. In total, Microsoft issued fixes for 51 vulnerabilities this week spread across 16 security bulletins, half of which were rated as important, the other eight being rated as critical.

The updates tackle vulnerabilities in Microsoft Edge and Internet Explorer, Windows, the Microsoft .NET Framework, and MS Office; however, it is the browser fixes that are the most important. These include actively exploited security vulnerabilities that can be used to compromise computers if users visit websites containing exploit kits.

Security update MS16-051 tackles the CVE-2016-0189 zero-day vulnerability in Internet Explorer, which if exploited, would allow an attacker to gain the same level of privileges as the current user. The flaw could be used to take control of the entire system. The exploit could be used to install new programs on the device, create new accounts, or modify or delete data. The vulnerability modifies the functioning of JScript and VBScript, changing how they handle objects in the computer’s memory.

The IE security vulnerability was brought to the attention of Microsoft by researchers at Symantec, who had discovered an active exploit that was being used alongside spear-phishing attacks in South Korea. Users were being directed to a website containing an exploit kit that had been updated with the IE security vulnerability.

The MS16-052 security update tackles a vulnerability in Microsoft Edge which similarly changes how objects in the memory are handled. These two updates should be prioritized by sysadmins, although all of the updates should be installed as soon as possible. Even the important updates could potentially be exploited and used to gain control of unpatched computers.

Bulletin MS16-054 is also a priority update to patch critical vulnerabilities in Adobe Flash. Since Flash is embedded in both Edge and IE, Microsoft has started issuing updates to address Adobe Flash vulnerabilities. While these security flaws are not believed to have been exploited in the wild, it will not be long before they are included in exploit kits.

Microsoft may have fixed its actively exploited security vulnerabilities, but despite Adobe issuing patches for Acrobat, ColdFusion, and Reader on Tuesday, Flash remains vulnerable to attack. Adobe has yet to issue a patch for an actively exploited Flash security vulnerability (CVE-2016-4117) that affects version and all earlier versions of the platform. This vulnerability has been included in exploit kits and can be used to take control of devices. In total, Adobe fixed 92 separate vulnerabilities in its Tuesday update.

Between Microsoft and Adobe, 143 vulnerabilities have been addressed this week. With hackers quick to add the vulnerabilities to website exploit kits, it is essential that patches are installed rapidly. These actively exploited security vulnerabilities also highlight the importance of using a web filtering solution to prevent users from visiting compromised websites where the vulnerabilities can be exploited.