CybersecurityMicrosoft patches CVE-2020-0674 Internet Explorer zero-day
Microsoft patched CVE-2020-0674 in February 2020—an IE zero-day being actively exploited. The scripting engine flaw lets attackers run code via malicious web content. If you still have IE deployed anywhere, patch now.
Editorially reviewed for factual accuracy
Microsoft released security updates for CVE-2020-0674 during February 2020 Patch Tuesday on 11 February 2020, addressing a critical use-after-free vulnerability in the Internet Explorer scripting engine that attackers had been actively exploiting in targeted attacks since early January. This vulnerability enabled remote code execution through malicious web content, affecting all Windows systems where Internet Explorer is installed regardless of whether IE serves as the primary browser. Organizations must focus on patching systems with IE components while evaluating long-term strategies for reducing IE exposure.
Vulnerability Technical Analysis
CVE-2020-0674 is a memory corruption vulnerability in the JScript scripting engine (jscript.dll) used by Internet Explorer. The vulnerability manifests as a use-after-free condition where the scripting engine improperly handles objects in memory, allowing attackers to corrupt memory in ways that enable arbitrary code execution.
The attack vector requires luring victims to malicious web pages containing specially crafted JavaScript that triggers the memory corruption. Successful exploitation achieves code execution with the privileges of the logged-on user. If the user has administrative privileges, attackers gain complete system compromise including ability to install programs, view and modify data, and create new privileged accounts.
Microsoft rated CVE-2020-0674 as Critical with a CVSS 3.0 base score of 7.5. The vulnerability affects the JScript9.dll component that processes JavaScript in Internet Explorer, making any system with IE installed potentially vulnerable regardless of browser usage patterns.
Exploitation techniques for use-after-free vulnerabilities in browser scripting engines have been refined over years of research. Sophisticated attackers maintain reliable exploit code for this class of vulnerability, enabling weaponization shortly after discovery.
Active Exploitation Campaign
Microsoft confirmed active in-the-wild exploitation before the February patch became available. Security Advisory ADV200001 published in January 2020 acknowledged targeted attacks while patches were still in development, creating an unusual situation where a critical vulnerability was publicly known without immediate remediation.
The exploitation was reportedly used in limited, targeted attacks suggesting nation-state or sophisticated criminal actor involvement. The precision targeting and operational sophistication required to maintain zero-day exploitation capability typically shows well-resourced threat actors rather than opportunistic attackers.
Security researchers linked the exploitation to threat actors associated with advanced persistent threat groups, though Microsoft did not publicly attribute the attacks. The combination of zero-day capability and targeted deployment suggests intelligence-gathering operations rather than financially motivated cybercrime.
The approximately one-month gap between exploitation discovery and patch availability created an extended exposure window. Organizations with valuable intellectual property or strategic significance faced heightened risk during this period, even with awareness of the threat.
Affected Systems and Scope
The vulnerability affects all Windows systems with Internet Explorer installed, spanning desktop and server platforms. Windows 10 systems across all supported versions including 1903, 1909, and earlier releases are affected. Windows 8.1 with IE11 and Windows 7 systems still running IE11 (though Windows 7 reached end of support in January 2020) require patching.
Windows Server platforms including Server 2008 R2, 2012, 2012 R2, 2016, and 2019 with IE installed need security updates. Servers often have IE components installed for administrative web interfaces even when browser usage is minimal.
Applications embedding Internet Explorer controls or using the MSHTML rendering engine may invoke vulnerable code paths even on systems where IE is never launched directly. Office applications, line-of-business applications with embedded browsers, and help systems using HTML rendering may expose the vulnerability.
Pre-Patch Mitigations
Before the February patch, Microsoft recommended temporary mitigations that organizations may have implemented. Modifying access control lists on jscript.dll to restrict execution prevented exploitation but caused compatibility issues with applications depending on JScript functionality.
Configuring Internet and Intranet zones to block Active Scripting or prompt before running scripts reduced exposure but impacted legitimate web application functionality. Organizations implemented these restrictions selectively based on user risk profiles and application requirements.
Exploit Guard and EMET configurations could make exploitation more difficult by enabling additional memory protections. Organizations that had previously deployed these protections gained defense-in-depth benefits during the vulnerability window.
Organizations that implemented temporary mitigations must verify proper rollback after patch installation to restore normal application functionality. Residual ACL restrictions could cause unexpected application failures if not removed after patching.
Enterprise Deployment Strategy
Patch deployment should focus on systems with elevated exploitation risk. Systems known to use Internet Explorer for business functions receive highest priority. Systems with administrative user accounts face escalated risk from privilege escalation following initial compromise.
Windows Server systems must be included in deployment scope despite typically lower browser usage. IE components on servers may be invoked by administrative interfaces, monitoring dashboards, or server applications rendering HTML content.
Application testing before broad deployment verifies that patches do not introduce regressions in line-of-business applications using IE components. Staged deployment to test groups enables identification of compatibility issues before production-wide rollout.
Endpoint management tools should verify patch deployment across the entire fleet. Vulnerability scanning can identify systems that failed to receive updates or where installation did not complete successfully.
Post-Patch Validation
After deploying security updates, you should confirm Internet Explorer version reflects the February 2020 cumulative update through version checking or inventory tools. Test applications that embed IE controls or use MSHTML rendering to verify continued functionality.
Remove any temporary ACL restrictions applied to jscript.dll during the pre-patch mitigation period. Verify Enhanced Security Configuration settings on servers remain appropriately configured after patching. Monitor for application compatibility issues that may require adjustment or workarounds.
Detection and Monitoring
Your security team should implement monitoring for exploitation attempts even after patching. Alert on Internet Explorer spawning unexpected child processes, making unusual network connections, or exhibiting memory corruption indicators. Monitor JScript execution from unusual contexts or by unexpected parent processes.
Review proxy logs for traffic to known exploit-hosting domains or suspicious redirect chains that might show exploitation attempts. Investigate IE crashes that could show exploitation attempts against either patched or unpatched systems. Correlate endpoint telemetry with threat intelligence on exploitation indicators.
Long-Term IE Risk Management
CVE-2020-0674 highlights ongoing security risks from Internet Explorer that you should address strategically. Develop migration plans to move legacy IE-dependent applications to modern browsers. Implement browser isolation for high-risk browsing scenarios requiring IE compatibility.
Configure Enterprise Mode Site Lists to limit IE usage to required internal sites, reducing exposure for general web browsing. Plan for IE11 deprecation as Microsoft shifts focus to Edge Chromium, accelerating modernization of applications with IE dependencies.
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Coverage intelligence
- Published
- Coverage pillar
- Cybersecurity
- Source credibility
- 73/100 — medium confidence
- Topics
- CVE-2020-0674 · Internet Explorer · Patch Tuesday
- Sources cited
- 3 sources (msrc.microsoft.com, portal.msrc.microsoft.com, iso.org)
- Reading time
- 6 min
Documentation
- Microsoft Security Update Guide: CVE-2020-0674 — Microsoft
- ADV200001 | Microsoft Guidance on Scripting Engine Memory Corruption Vulnerability — Microsoft
- ISO/IEC 27001:2022 — Information Security Management Systems — International Organization for Standardization
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