Microsoft Patch Tuesday, August 2020 Edition

An elevation of privilege vulnerability exists when the Windows Print Spooler service improperly allows arbitrary writing to the file system. An attacker who successfully exploited this vulnerability could run arbitrary code with elevated system privileges. An attacker could then install programs; view, change, or delete data; or create new accounts with full user rights. To exploit this vulnerability, an attacker would have to log on to an affected system and run a specially crafted script or application. The update addresses the vulnerability by correcting how the Windows Print Spooler Component writes to the file system.

An elevation of privilege vulnerability exists when the Windows Print Spooler service improperly allows arbitrary writing to the file system. An attacker who successfully exploited this vulnerability could run arbitrary code with elevated system privileges. An attacker could then install programs; view, change, or delete data; or create new accounts with full user rights. To exploit this vulnerability, an attacker would have to log on to an affected system and run a specially crafted script or application. The update addresses the vulnerability by correcting how the Windows Print Spooler Component writes to the file system.

CVE-2020-1380 is a memory corruption vulnerability (an out-of-bounds write, CWE-787) in the Microsoft Internet Explorer scripting engine that can corrupt memory when the engine processes maliciously crafted script content. It is triggered by luring a user to visit an attacker-controlled or compromised web page in Internet Explorer or in an application that invokes the IE engine, with no authentication required. Successful exploitation allows the attacker to execute arbitrary code in the context of the current user, gaining that user's privileges on the system. All installations of the affected Microsoft Internet Explorer versions are potentially exposed, with the greatest risk to legacy and enterprise Windows systems that still browse or render content with IE. The flaw is on CISA's Known Exploited Vulnerabilities catalog (added 2021-11-03), indicating exploitation in the wild, while no public proof-of-concept is known and ransomware use is unconfirmed.

Do: Apply Microsoft's June 2020 (or later) Windows cumulative security updates on every system running Internet Explorer, per the vendor instructions cited by CISA. Given the KEV listing (added 2021-11-03) and high EPSS (~24% 30-day exploitation probability, 98th percentile), treat this as a priority patch. Reduce attack surface by steering users to Microsoft Edge instead of IE for web browsing and auditing internal apps or legacy sites that still invoke the IE engine to render external content.

CVE-2020-1464 is a spoofing vulnerability in Microsoft Windows caused by improper validation of file digital signatures (CWE-347). It is triggered when Windows accepts a file whose signature is malformed or improperly formed, treating it as validly signed. An attacker who can introduce such a file onto a system can bypass security features that depend on signature verification, allowing improperly signed files to load as if trusted — a common technique for malware delivery and defense evasion. Essentially all Microsoft Windows deployments on affected versions are exposed until patched. The flaw is listed in CISA's Known Exploited Vulnerabilities catalog (added 2021-11-03), confirming exploitation in the wild, though no public proof-of-concept is known and any ransomware linkage is unconfirmed.

Do: Apply Microsoft's security updates for CVE-2020-1464 on all Windows systems per vendor instructions, prioritizing internet-facing and high-value endpoints, and verify patch coverage fleet-wide given the CISA KEV listing. Until patched, avoid relying solely on digital-signature-based trust decisions (e.g., application allowlisting or signature-gated file loading) for files of unknown origin.

CVE-2020-1472, widely known as "Zerologon," is an elevation-of-privilege flaw in how the Netlogon secure channel is established over the Netlogon Remote Protocol (MS-NRPC) on Microsoft domain controllers. An unauthenticated attacker with network reachability to a domain controller sends specially crafted Netlogon messages to establish a vulnerable secure channel and then runs a specially crafted application on the network to obtain domain administrator access. Successful exploitation yields domain administrator privileges, effectively full compromise of the Active Directory environment, and the flaw is known to be used in ransomware operations. Any organization running affected Windows Server versions (2008 through 20H2) as domain controllers is exposed, along with environments using Netlogon implementations from Samba and distributions or products from Fedora, openSUSE, Canonical (Ubuntu), Debian, Synology, and Oracle. Exploitation is highly active: a public Zerologon PoC/exploit is available, the flaw is on CISA's Known Exploited Vulnerabilities catalog (added 2021-11-03, with known ransomware use), and EPSS estimates a 99.4% probability of exploitation within 30 days.

Do: Apply the vendor updates on all domain controllers and other affected systems immediately, following Microsoft's two-phase Netlogon secure channel guidance (the enforcement phase of the phased rollout began in Q1 2021). Audit Netlogon secure-channel connections and event logs for clients still using vulnerable connections before enabling full enforcement, and install updated packages for Samba and other Netlogon implementations from Fedora, openSUSE, Ubuntu, Debian, Synology, and Oracle. Given known ransomware use, prioritize patching any domain controller reachable from user networks, VPNs, or the internet.