Which vulnerabilities were most exploited by cybercriminals in 2019?

CVE-2012-0158 is a remote code execution flaw in Microsoft's MSCOMCTL.OCX, the Windows Common Controls ActiveX component, where improper handling of crafted input allows memory corruption and code execution. It is typically triggered when an application that uses the control (most commonly Microsoft Office) processes specially crafted content, such as a malicious document or file, meaning a victim usually has to open attacker-supplied content. Successful exploitation lets an attacker run arbitrary code and take complete control of the affected system with the privileges of the current user. Any Windows system carrying a vulnerable copy of MSCOMCTL.OCX — including systems where the control was redistributed by legacy applications — is affected, which makes the potential population very large. Exploitation is confirmed and ongoing: the flaw is in CISA's Known Exploited Vulnerabilities catalog (added 2021-11-03) with known ransomware use, and EPSS assigns it the maximum reported probability of exploitation within 30 days.

Do: Apply the Microsoft security update for MSCOMCTL.OCX (per vendor instructions, per CISA's required action) on all systems, prioritizing endpoints and servers that open Office documents. Because exploitation commonly arrives via malicious documents, treat unsolicited Office/RTF attachments with suspicion and verify that applications that redistribute MSCOMCTL.OCX have installed a patched copy. Scan the estate for the presence and version of MSCOMCTL.OCX, especially on legacy Windows/Office installations that may be missed by routine patching.

CVE-2015-2419 is a memory corruption flaw (CWE-119) in the JScript engine used by Microsoft Internet Explorer, allowing remote attackers to execute arbitrary code or cause a denial of service through a crafted website. It is triggered when a user visits an attacker-controlled page whose JScript content corrupts memory in the affected browser process. A successful attacker gains remote code execution in the context of the logged-on user (or crashes the browser), which makes drive-by and exploit-kit delivery routes viable. Any Windows user running the affected versions of Internet Explorer at the time of disclosure was exposed, and Microsoft shipped fixes as part of its July 2015 security updates. The flaw is listed in CISA's Known Exploited Vulnerabilities catalog (added 2022-03-28), carries a 53.4% EPSS (99th percentile), and related reporting places it among the top vulnerabilities used by exploit kits in 2015-2016.

Do: Apply Microsoft's July 2015 security updates for Internet Explorer per vendor instructions, as required by the CISA KEV catalog, and verify that any legacy Windows systems still running Internet Explorer have received them. Because exploitation typically occurs via drive-by web attacks, retire or fully patch IE on client endpoints and keep endpoint protection enabled to catch exploit-kit delivery. Confirm no workstations remain on unpatched IE builds, since this entry has been in CISA KEV since March 2022 and exploitation probability remains high (EPSS 53.4%).

CVE-2017-0199 is a remote code execution vulnerability in Microsoft Office and WordPad that stems from improper parsing of specially crafted files. Attackers trigger it by getting a user to open a malicious document, after which attacker-controlled code executes with the privileges of the logged-in user. Anyone running the affected Microsoft Office or WordPad software is exposed, and CISA notes the flaw has been leveraged in ransomware campaigns; no CVSS score is available in the source data. The flaw was added to CISA's Known Exploited Vulnerabilities catalog on 2021-11-03, and EPSS assigns a 99.9% probability of exploitation within 30 days (100th percentile), indicating active, ongoing exploitation.

Do: Apply Microsoft's security updates for Office and Windows per vendor instructions, as required by CISA's KEV catalog; the flaw was publicly reported as fixed in Microsoft's April 2017 security updates. Until patched, treat unsolicited Office documents and email attachments as high-risk, since exploitation requires a user to open a crafted file. Verify that all Office and WordPad installations across the estate—especially endpoints that handle untrusted documents—have received the update.

CVE-2017-11882 is a memory corruption vulnerability (CWE-119) in Microsoft Office, residing in the legacy Microsoft Equation Editor component (EQNEDT32.EXE), that allows remote code execution in the context of the current user. Attackers trigger it by persuading a user to open a crafted document, most commonly an RTF file or other Office document carrying a malicious embedded equation object, which overflows a buffer while the equation content is parsed. Successful exploitation lets the attacker run arbitrary code with the privileges of the signed-in user, a typical foothold for malware delivery and, per CISA, for ransomware operations. Any environment running affected Microsoft Office builds is exposed; the source data does not enumerate specific affected version ranges. The flaw is confirmed exploited in the wild: it was added to the CISA Known Exploited Vulnerabilities catalog on 2021-11-03 with known ransomware use and holds a 99.9% EPSS score (percentile 100), though the source data lists no public PoC.

Do: Apply Microsoft's Office security updates (November 2017 or later) across all endpoints, prioritizing this KEV-listed flaw given its known ransomware use. On systems that cannot yet be patched, disable or unregister the legacy Equation Editor (EQNEDT32.EXE) and consider blocking or warning on RTF attachments as interim mitigations. Check for indicators of abuse such as EQNEDT32.EXE spawning unexpected child processes after document opens.

Internet Explorer in Microsoft Windows 7 SP1, Windows Server 2008 R2 SP1, Windows 8.1 and Windows RT 8.1, Windows Server 2012 R2, and Microsoft Edge and Internet Explorer in Windows 10 Gold, 1511, 1607, 1703, and Windows Server 2016 allow an attacker to execute arbitrary code in the context of the current user due to the way that Microsoft browsers access objects in memory, aka "Microsoft Browser Memory Corruption Vulnerability".

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.

WinRAR versions through 5.61 contain a path traversal flaw (CWE-22, also mapped to CWE-36) in the UNACEV2.dll library used to unpack ACE-format archives: when a crafted archive's filename field contains absolute-path patterns, WinRAR ignores the user-selected extraction destination and writes the file to any absolute path the attacker specifies. It is triggered by inducing a user to open a malicious ACE archive (user interaction required), allowing arbitrary file placement on the endpoint — for example, writing an executable to a Windows startup folder to achieve code execution at next logon, as demonstrated in the original Check Point research. Only RARLAB WinRAR is affected, and the issue was assigned by Check Point acting as CNA, with multiple public proofs of concept available. Exploitation is well established: the flaw is on CISA's Known Exploited Vulnerabilities catalog (added 2022-02-15) with known ransomware use (e.g., JNEC.a delivered via this exploit), has been linked to targeted-activity by threat actors, and EPSS currently assigns a 96.3% probability of exploitation within 30 days. Because WinRAR lacks an automatic update mechanism, stale installations remained exposed and under active attack long after the vendor fix was published.

Do: Apply updates per vendor instructions by upgrading to a WinRAR release newer than 5.61, in which the vulnerable ACE handling is patched or replaced; ensure endpoints actually run the updated build given WinRAR does not auto-update. If patching cannot be done promptly, delete or neutralize UNACEV2.dll (disabling ACE extraction) or unpack ACE archives with a patched alternative, and scrutinize ACE attachments arriving via email. Hunt for unexpected files dropped into auto-run locations (e.g., startup folders) and treat this as a KEV entry with the corresponding federal remediation deadline.

CVE-2018-4878 is a use-after-free (CWE-416) in Adobe Flash Player before 28.0.0.161, caused by a dangling pointer in the Primetime SDK's media-player handling of listener objects. An attacker triggers it by persuading a user to open attacker-controlled Flash content — typically a malicious SWF delivered via email, Office documents, or malvertising/exploit kits — because the CVSS vector (AV:L, UI:R) requires local user interaction. Successful exploitation yields arbitrary code execution with the privileges of the user running Flash. Anyone running a vulnerable Flash Player was exposed, including Red Hat Enterprise Linux Desktop/Server/Workstation users running Red Hat's packaged Flash plugin. The flaw was exploited as a zero-day in January–February 2018 (documented by McAfee and distributed alongside the Fallout exploit kit), and it remains in CISA's KEV with known ransomware use.

Do: Upgrade Adobe Flash Player to 28.0.0.161 or later, including Red Hat's flash-plugin package on RHEL Desktop/Server/Workstation. Because Flash is now end-of-life, CISA's required KEV action is to remove or disconnect Flash entirely where still in use — audit browsers, Office configurations, and legacy RHEL hosts for residual Flash installs, and block SWF content delivered via email and the web. Given confirmed in-the-wild exploitation, known ransomware use, and 89.5% EPSS, prioritize this in remediation tracking.

CVE-2018-8174 is an out-of-bounds write (CWE-787) in the Microsoft Windows VBScript engine, caused by the way it handles objects in memory. An attacker triggers it by convincing a user to visit a specially crafted website or open crafted content that invokes the VBScript engine (for example via Internet Explorer or a document preview), requiring user interaction. Successful exploitation yields remote code execution with the privileges of the logged-on user, enabling program installation, data theft and account takeover. All listed Windows client and server releases are affected: Windows 7, 8.1, RT 8.1, Windows 10 (1607-1803), and Windows Server 2008/2008 R2, 2012/2012 R2, 2016. Exploitation is in the wild: the flaw was fixed in the May 2018 Patch Tuesday, is listed in CISA KEV with known ransomware use, and public PoCs (0patch, ExploitDB 44741) and exploit kit usage have been documented; EPSS puts its 30-day exploitation probability at 88.5%.

Do: Apply Microsoft's May 2018 security updates (and any later cumulative or Extended Security Updates) to every listed Windows client and server release, as required by the CISA KEV listing, prioritizing internet-reachable and user-facing systems given known ransomware use. Upgrade out-of-support platforms (Windows 7/8.1/RT 8.1, Server 2008/2008 R2, 2012/2012 R2) to supported builds or ensure ESU coverage. As interim mitigation, block VBScript execution in Internet Explorer web zones using Microsoft's documented Group Policy/registry settings, and hunt for prior exploitation on legacy systems.

CVE-2019-0752 is a type confusion (CWE-843) memory corruption vulnerability in the way the scripting engine used by Internet Explorer handles objects in memory, and it is distinct from the related scripting-engine flaws CVE-2019-0739, CVE-2019-0753, and CVE-2019-0862. An attacker triggers it by convincing a user to view attacker-controlled or attacker-crafted web content in Internet Explorer, where malformed handling of in-memory objects corrupts memory (the CVSS vector reflects a network attack requiring user interaction with high attack complexity). Successful exploitation yields remote code execution with the privileges of the current user, giving the attacker high confidentiality, integrity, and availability impact on the host. Anyone running Internet Explorer on supported Windows client or server systems is exposed; the provided data does not specify exact affected version ranges, though the public proof-of-concept was demonstrated on Windows 10 1809 (build 17763.316). Exploitation is confirmed in the wild: the flaw is in CISA's Known Exploited Vulnerabilities catalog (added 2022-02-15) with known ransomware use, carries a top-percentile EPSS score of 81.6%, and contemporary reporting ties scripting-engine flaws like this to exploit kits (e.g., RIG) delivering malware such as Dridex.

Do: Apply Microsoft's security updates that address CVE-2019-0752 via Windows Update or WSUS, per the CISA KEV required action, and audit legacy Windows clients and servers for any that have not been patched. Where updates are impractical (e.g., out-of-support systems), stop using Internet Explorer as the default browser, restrict or disable scripting in the Internet zone, and consider blocking IE-facing access to untrusted sites. Because exploit kits (e.g., RIG) and ransomware operators have leveraged IE scripting-engine flaws, prioritize patching user workstations and shared/multi-user systems.

CVE-2019-0841 is a local privilege escalation flaw in the Windows AppX Deployment Service (AppXSVC), which handles deployment of packaged (AppX) applications. The service improperly handles hard links (CWE-59), letting a local attacker manipulate hard links so that AppXSVC performs file operations in protected locations with elevated rights. A successful exploit allows the attacker to run processes in an elevated context — effectively administrative/SYSTEM privileges — which ransomware operators have used in chained attacks. Any unpatched Microsoft Windows system is potentially affected; the available data lists only 'Microsoft Windows' without specific version ranges, so defenders should consult Microsoft's advisory for exact affected releases. The vulnerability was added to CISA's Known Exploited Vulnerabilities catalog on 2022-03-15 with known ransomware use, and EPSS assigns a 41.4% probability of exploitation within 30 days (99th percentile), although no public proof-of-concept is catalogued.

Do: Apply Microsoft's Windows cumulative updates per vendor instructions as the KEV required action, prioritizing systems where users can log on locally, since exploitation requires local access; the fix shipped in Microsoft's April 2019 security release, so confirm no hosts remain on older builds. Because ransomware operators chain this local privilege escalation, verify patch status across the estate with your inventory tooling and monitor for unexpected elevation or hard-link manipulation on AppXSVC as interim risk reduction.

Atlassian Confluence Server and Data Center contain a server-side template injection flaw (CWE-22) in which attacker-supplied template content is processed by the server, enabling path traversal and ultimately remote code execution. An attacker triggers it by submitting crafted template syntax in a request to a vulnerable instance, and can run arbitrary commands or code on the underlying server. Successful compromise could allow data theft, deployment of webshells, or ransomware; CISA notes known ransomware use of this vulnerability. Organizations running self-hosted Confluence Server or Data Center are affected, particularly instances exposed to the internet. Exploitation is confirmed in the wild: the flaw is in CISA's Known Exploited Vulnerabilities catalog (added 2021-11-03) and EPSS assigns a 99.9% probability of exploitation, placing it in the top percentile.

Do: Apply updates per vendor instructions by upgrading Confluence Server and Data Center to Atlassian's fixed releases, and prioritize internet-facing instances. Until patched, restrict network exposure of Confluence and monitor for signs of compromise such as webshells, unexpected processes, or ransomware activity, since ransomware operators are known to exploit this flaw.