Microsoft tackled 53 vulnerabilities with today’s Patch Tuesday bulletin. Remote code execution bugs dominated this month’s patches, representing 25 fixes. In total, 20 of Microsoft’s security fixes were rated critical.

Notable are four vulnerabilities with public exploits identified by Microsoft as CVE-2017-11848, CVE-2017-11827, CVE-2017-11883 and CVE-2017-8700. But, according to an analysis of Patch Tuesday fixes by Qualys, none of the four are being used in active campaigns.

Security experts say companies should prioritize patching a half-dozen scripting engine memory corruption vulnerabilities impacting Microsoft’s Edge and Internet Explorer 11 browsers running on versions of Windows 10, Windows 8.1 , Windows 7 and Windows Server (version 1709).

“A remote code execution vulnerability exists in the way the scripting engine handles objects in memory in Microsoft browsers. The vulnerability could corrupt memory in such a way that an attacker could execute arbitrary code in the context of the current user,” wrote Microsoft regarding CVE-2017-11836, CVE-2017-11837, CVE-2017-11838, CVE-2017-11839, CVE-2017-11871, and CVE-2017-11873.

Microsoft said if exploited, an attacker could gain the same user rights as the current user. “In a web-based attack scenario, an attacker could host a specially crafted website that is designed to exploit the vulnerability through Microsoft Edge and then convince a user to view the website,” Microsoft wrote. “These websites could contain specially crafted content that could exploit the vulnerability.”

Researchers at Zero Day Initiative said that of the critical vulnerabilities it spotted, a distinct malware bypass theme emerged. It wrote, “CVE-2017-11830 patches a Device Guard security feature bypass vulnerability that would allow malware authors to falsely authenticated files… CVE-2017-11877 fixes an Excel security feature bypass vulnerability that fails to enforce macro settings, which are often used by malware developers.”

“Speaking of malware, this patch fixes a CVE (CVE-2017-11830) that allows Device Guard to incorrectly validates an untrusted file. This means attackers could make an unsigned file appear to be signed. Since Device Guard relies on a valid signature to determine trustworthiness, malicious files could be executed by making untrusted files seem trusted. This is exactly the sort of bug malware authors seek, as it allows them to have their exploit appear as a trusted file to the target,” ZDI wrote.

Part of Patch Tuesday also included an advisory (ADV170020), which is related to Microsoft Office Defense in Depth Update series. “ADV170020 is likely related to the malware abusing Dynamic Data Exchange, and this advisory may help restrict abusing this protocol feature,” wrote Zero Day Initiative researchers.

Despite a number of attacks that have used Dynamic Data Exchange fields in Office, Microsoft has remained insistent that DDE is a product feature and not a vulnerability.

Part of Patch Tuesday also includes something new, according to Greg Wiseman, Rapid7’s senior security researcher, who said Microsoft is applying fixes to some of its open source projects. “Sixteen of the Edge vulnerabilities have been resolved in ChakraCore, the open source part of Edge’s JavaScript engine,” Wiseman said. “.NET Core is being patched for a denial of service (DoS) vulnerability (CVE-2017-11770), and ASP.NET Core has fixes for DoS (CVE-2017-11883), privilege escalation (CVE-2017-11879), and information disclosure (CVE-2017-8700) vulnerabilities this month.”

Lastly, Qualys warns (CVE-2017-11882), a Microsoft Office memory corruption vulnerability rated as important, should be prioritized. “There may be POC code for this vulnerability, so it is recommended that you give the Office updates attention this month as well,” Qualys wrote.