December 2018 Patch Tuesday: Microsoft patches Windows zero-day exploited in the wild

CVE-2018-15982 is a use-after-free flaw (CWE-416) in Adobe Flash Player versions 31.0.0.153 and earlier, and 31.0.0.108 and earlier, in which Flash frees memory that is subsequently reused, corrupting process memory. It is triggered when Flash processes crafted Flash content, most notably embedded in Microsoft Office documents, requiring a user to open or view the malicious content (CVSS attack vector is local with user interaction required). Successful exploitation gives the attacker arbitrary code execution with the privileges of the user viewing the content. Affected users include anyone running the listed Flash Player versions, including the Flash Player Installer and the Adobe-supplied Flash plugin shipped with Red Hat Enterprise Linux Desktop, Server and Workstation. Exploitation is confirmed in the wild: the flaw is in CISA's Known Exploited Vulnerabilities catalog (added 2022-02-15) with known ransomware use, a public exploit is available on Exploit-DB, and EPSS assigns a top-percentile 89.1% probability of exploitation within 30 days.

Do: Flash Player is end-of-life: per CISA's required action, remove or disconnect Flash wherever it is still in use; if Flash must remain, update beyond the affected 31.0.0.153/31.0.0.108 builds and update the flash-plugin package on Red Hat Enterprise Linux. Mitigate the known delivery vector by blocking or disabling embedded Flash (SWF) content in Microsoft Office documents and mail clients, and hunt for suspicious documents with embedded Flash given the known in-the-wild and ransomware use.

Adobe Acrobat and Reader versions 2019.008.20081 and earlier, 2019.008.20080 and earlier, 2019.008.20081 and earlier, 2017.011.30106 and earlier version, 2017.011.30105 and earlier version, 2015.006.30457 and earlier, and 2015.006.30456 and earlier have a heap overflow vulnerability. Successful exploitation could lead to arbitrary code execution.

CVE-2018-8589 is an elevation of privilege vulnerability in Win32k.sys, the Windows kernel-mode component that handles system calls, affecting Windows 7, Windows Server 2008, and Windows Server 2008 R2. It is triggered when Windows improperly handles calls to Win32k.sys, allowing a local attacker who is already able to execute low-privileged code (for example, via a malicious application or as a second stage of a browser exploit) to escalate privileges. A successful exploit grants the attacker elevated (kernel/SYSTEM-level) privileges on the local machine, typically enabling full control and often chained with code-execution bugs. Windows 7 and Windows Server 2008/2008 R2 users and administrators are affected; the flaw was patched in Microsoft's November 2018 security updates. The vulnerability was known to be actively exploited in the wild at the time of the November 2018 Patch Tuesday, and it is listed in CISA's Known Exploited Vulnerabilities catalog (added May 23, 2022), with EPSS at roughly 3% (87th percentile).

Do: Apply the Microsoft November 2018 security updates (or later) to all Windows 7, Windows Server 2008, and Windows Server 2008 R2 systems, per the CISA KEV required action. Because Windows 7 and Server 2008 are past end of support, verify patch status on legacy/extended-support (ESU) systems, inventory any remaining unpatched hosts, and prioritize upgrading them; until patched, limit execution of untrusted local code and keep kernel exploit mitigations enabled.

CVE-2018-8611 is an elevation-of-privilege vulnerability in the Microsoft Windows kernel caused by improper handling of objects in memory (recorded as CWE-404, improper resource shutdown/release). It is a local flaw: an attacker who can already run code with limited privileges on a target machine can trigger it with a specially crafted application, with no user interaction required. Successful exploitation executes code in kernel context, elevating the attacker to SYSTEM/administrator and giving full control of the host, a typical post-initial-access step in ransomware chains. Nearly every Windows client and server version in support at disclosure is affected: Windows 7, 8.1, RT 8.1 and Windows 10 (1607 through 1809), plus Windows Server 2008 through 2019. The flaw is confirmed exploited in the wild, with CISA adding it to the KEV catalog on 2022-05-24 and an EPSS of 4.2% (90th percentile); the KEV record lists ransomware use as unknown, though public reporting ties a family of Windows kernel EoP exploits including this one to ransomware operators.

Do: Apply Microsoft's December 2018 security update for CVE-2018-8611 on all affected Windows 7, 8.1, RT 8.1, 10 and Server 2008-2019 hosts; there is no known workaround and patching is the required CISA KEV action, so verify the December 2018 (or later) monthly rollup is installed. Prioritize servers and workstations where limited-privilege users or untrusted workloads run (RDS, application servers, shared endpoints), and treat any remaining unpatched Windows 7/8.1/legacy-Server machine as high risk because ransomware operators have been observed chaining Windows kernel EoP exploits like this one after initial access.

A remote code execution vulnerability exists in Windows Domain Name System (DNS) servers when they fail to properly handle requests, aka "Windows DNS Server Heap Overflow Vulnerability." This affects Windows Server 2012 R2, Windows Server 2019, Windows Server 2016, Windows 10, Windows 10 Servers.