CriticalCVE-2018-8174

Microsoft Windows VBScript Engine Out-of-Bounds Write Vulnerability (CVE-2018-8174)

Published 09.05.2018In CISA KEV since 15.02.2022Sources: CVE.org

What is affected, what to do

A remote code execution vulnerability exists in the way that the VBScript engine handles objects in memory, aka "Windows VBScript Engine Remote Code Execution Vulnerability." This affects Windows 7, Windows Server 2012 R2, Windows RT 8.1, Windows Server 2008, Windows Server 2012, Windows 8.1, Windows Server 2016, Windows Server 2008 R2, Windows 10, Windows 10 Servers.

The vulnerability is being actively exploited; treat it as a priority. CISA lists it as used in ransomware campaigns. The available sources name no fixed version. Check the vendor guidance in the references below. Immediate actions, mitigation and detection rules are in the runbook below.

Affected: Microsoft Windows 7 eq 32-bit Systems Service Pack 1..32-bit Systems Service Pack 1
Microsoft Windows 7 eq x64-based Systems Service Pack 1..x64-based Systems Service Pack 1
Microsoft Windows Server 2012 R2 eq (Server Core installation)..(Server Core installation)
Microsoft Windows RT 8.1 eq Windows RT 8.1..Windows RT 8.1
Microsoft Windows Server 2008 eq 32-bit Systems Service Pack 2..32-bit Systems Service Pack 2
Microsoft Windows Server 2008 eq 32-bit Systems Service Pack 2 (Server Core installation)..32-bit Systems Service Pack 2 (Server Core installation)
Microsoft Windows Server 2008 eq Itanium-Based Systems Service Pack 2..Itanium-Based Systems Service Pack 2
Microsoft Windows Server 2008 eq x64-based Systems Service Pack 2..x64-based Systems Service Pack 2
Microsoft Windows Server 2008 eq x64-based Systems Service Pack 2 (Server Core installation)..x64-based Systems Service Pack 2 (Server Core installation)
Microsoft Windows Server 2012 eq (Server Core installation)..(Server Core installation)
Microsoft Windows 8.1 eq 32-bit systems..32-bit systems
Microsoft Windows 8.1 eq x64-based systems..x64-based systems
Microsoft Windows Server 2016 eq (Server Core installation)..(Server Core installation)
Microsoft Windows Server 2008 R2 eq Itanium-Based Systems Service Pack 1..Itanium-Based Systems Service Pack 1
Microsoft Windows Server 2008 R2 eq x64-based Systems Service Pack 1..x64-based Systems Service Pack 1
Microsoft Windows Server 2008 R2 eq x64-based Systems Service Pack 1 (Server Core installation)..x64-based Systems Service Pack 1 (Server Core installation)
Microsoft Windows 10 eq 32-bit Systems..32-bit Systems
Microsoft Windows 10 eq Version 1607 for 32-bit Systems..Version 1607 for 32-bit Systems
Microsoft Windows 10 eq Version 1607 for x64-based Systems..Version 1607 for x64-based Systems
Microsoft Windows 10 eq Version 1703 for 32-bit Systems..Version 1703 for 32-bit Systems
Microsoft Windows 10 eq Version 1703 for x64-based Systems..Version 1703 for x64-based Systems
Microsoft Windows 10 eq Version 1709 for 32-bit Systems..Version 1709 for 32-bit Systems
Microsoft Windows 10 eq Version 1709 for x64-based Systems..Version 1709 for x64-based Systems
Microsoft Windows 10 eq Version 1803 for 32-bit Systems..Version 1803 for 32-bit Systems
Microsoft Windows 10 eq Version 1803 for x64-based Systems..Version 1803 for x64-based Systems
Microsoft Windows 10 eq x64-based Systems..x64-based Systems
Microsoft Windows 10 Servers eq version 1709 (Server Core Installation)..version 1709 (Server Core Installation)
Microsoft Windows 10 Servers eq version 1803 (Server Core Installation)..version 1803 (Server Core Installation)

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Metrics

7.5

Priority

XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.

Source: NVD, CVSS v3

7.5

CVSS v3

Severity High on the scale from 0 to 10.

Source: CVE.org

88.2 %

EPSS score

High — model estimates ≥ 50% chance of real-world exploitation within 30 days.

Source: FIRST EPSS, percentile 99.77

Show all metrics

Severity: Critical
Priority (0–325) The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first? Read in glossary: 242.13 Methodology
Exploit maturity An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack. Read in glossary: actively exploited
XIEM Effective CVSS XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command. Read in glossary: 7.5 Methodology
CVSS v3 CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions. Read in glossary: 7.5
EPSS score The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“. Read in glossary: 88.2 %; High — model estimates ≥ 50% chance of real-world exploitation within 30 days.
EPSS percentile The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking. Read in glossary: 99.77; Critical — this CVE ranks in the top fifth of all CVEs scored today (rank ≥ 80%).
KEV status The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching. Read in glossary: Actively exploited
Published: 09.05.2018
In CISA KEV since The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching. Read in glossary: 15.02.2022
CISA assessment (SSVC): Exploitation: active · not automatable · Technical impact: total; Source: CISA Vulnrichment, as of 14 February 2022
CWE CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect. Read in glossary: CWE-787

Response and mitigation

Why act now?

Prioritisation rationale

This flaw gives an attacker network-reachable code execution in user context without authentication. The only requirement is a single user interaction: opening a crafted Office document or rendering a page through the IE engine. That made it a staple of exploit kits and targeted phishing, and CISA explicitly flags it for known ransomware use. Its exploitation likelihood ranks among the very highest of all CVEs, and the nominally high attack complexity is no real barrier for mature exploit chains. Treat it as top priority if you still run Windows 7, Server 2008 or unpatched Windows 10 builds, or depend on IE11 or IE-mode line-of-business apps. In fully patched estates, verifying patch state and enforcing the ASR rules is sufficient.

01
Runbook step 1
Immediate response (0-24 h)
- Deploy the Microsoft security update for the VBScript engine to every affected system: Windows 7, 8.1, RT 8.1, 10 (1607/1703/1709/1803) and Server 2008, 2008 R2, 2012, 2012 R2 and 2016. The fix shipped in the May 2018 Patch Tuesday release; look up the per-build KB number in the vendor advisory. Verify compliance via WSUS/Intune/SCCM against your asset inventory, not assumptions.
- Identify hosts that cannot be patched, especially Windows 7 and Server 2008 without ESU. Cut them off from web browsing and inbound email, or move them into an isolated segment.
- Disable VBScript in Internet Explorer via GPO. Set "Allow VBScript to run in Internet Explorer" to Disabled for the Internet and Restricted Sites zones under Computer Configuration → Administrative Templates → Windows Components → Internet Explorer → Internet Control Panel → Security Page. Alternatively, set URL action 140C = 3.
- Remove or disable the Internet Explorer 11 optional feature wherever it is not business-critical. Handle legacy app dependencies through Edge IE mode with a controlled site list.
- Sweep recent mailboxes for Office documents (RTF/DOCX) carrying embedded URL monikers or OLE links to external HTML resources, and quarantine any hits.
02
Runbook step 2
Mitigation layers
- Endpoint hardening (Microsoft Defender ASR): Enable these rules in block mode:
  
  "Block all Office applications from creating child processes" (D4F940AB-401B-4EFC-AADC-AD5F3C50688A)
  
  "Block JavaScript or VBScript from launching downloaded executable content" (D3E037E1-3EB8-44C8-A917-57927947596D)
- Office configuration: Enforce Protected View for internet-sourced files and attachments. Use File Block Settings to block RTF and legacy formats from external sources, and block internet-originating macros by GPO.
- Mail and web gateway: Detonate RTF/DOC attachments containing objdata/\objautlink, and documents with OLE links to http(s)://… HTML pages, in a sandbox. At the proxy, block HTML responses containing language="vbscript" or <script type="text/vbscript"> for internet-zone traffic.
- Network segmentation: Servers (2008–2016) should never browse freely. Force outbound HTTP/HTTPS through an authenticating, category-filtering proxy, and drop direct TCP 80/443 egress from server VLANs.
- Least privilege: Run end users without local admin rights (use LAPS for local admin accounts). Second-stage payloads then stay confined to user context.
- Application control: Use WDAC/AppLocker to block execution from %TEMP%, %APPDATA% and Downloads. This breaks the typical post-exploit dropper stage.
03
Runbook step 3
Detection rules
- Sysmon EID 7 / MDE image load: An Office process loading vbscript.dll points to the URL-moniker exploit path. KQL: DeviceImageLoadEvents | where FileName =~ "vbscript.dll" and InitiatingProcessFileName in~ ("winword.exe","excel.exe","powerpnt.exe","outlook.exe")
- Process ancestry (Sysmon EID 1 / Security 4688): Watch for iexplore.exe, winword.exe or excel.exe spawning cmd.exe, powershell.exe, mshta.exe, rundll32.exe, regsvr32.exe or certutil.exe. Sigma shape: ParentImage|endswith: [\iexplore.exe, \winword.exe] AND Image|endswith: [\powershell.exe, \cmd.exe, \mshta.exe, \rundll32.exe]
- Proxy / web logs: Look for an Office user agent (e.g. ms-office) fetching an HTML page right after an attachment is opened. Also flag HTML responses whose VBScript contains Class_Terminate alongside large ReDim operations. SPL idea: index=proxy http_user_agent="*ms-office*" content_type="text/html"
- File creation (Sysmon EID 11): Flag executables (.exe, .dll, .scr) written to %TEMP% or %APPDATA% by iexplore.exe or Office processes shortly after a network connection (Sysmon EID 3).
- Network (Zeek/Suricata): Enable the public ET signatures covering CVE-2018-8174 and VBScript exploit-kit landing pages. Hunt http.log for Office processes contacting newly seen, low-reputation domains.

Detection rules

No NEOSEC detection rule is available for this vulnerability yet.

Classification under NIS2 and CRA

Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

NIS2 NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management. Read in glossary: Actively exploited: treat the vulnerability as a priority in vulnerability handling under Art. 21(2)(e) NIS2. If it is exploited in your environment, check the reporting obligation under Art. 23 (early warning within 24 hours).
CRA The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates. Read in glossary: Since 11.09.2026, manufacturers of affected products with digital elements must report actively exploited vulnerabilities under Art. 14 CRA, with an early warning within 24 hours via ENISA's single reporting platform.
ISO/IEC 27001 ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security. Read in glossary: Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

Description

Source: CISA KEV Catalog, cvelistv5, NVD (NIST)

Affected products

The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.

Affected products
		Affected versions	Fixed in
Microsoft	Windows 10	`32-bit Systems` `Version 1803 for 32-bit Systems` `x64-based Systems` `Version 1703 for 32-bit Systems` `Version 1709 for 32-bit Systems` `Version 1803 for x64-based Systems` `Version 1607 for 32-bit Systems` `Version 1703 for x64-based Systems` `Version 1709 for x64-based Systems` `Version 1607 for x64-based Systems`	— — — — — — — — — —
Microsoft	Windows 10 Servers	`version 1803 (Server Core Installation)` `version 1709 (Server Core Installation)`	— —
Microsoft	Windows 7	`32-bit Systems Service Pack 1` `x64-based Systems Service Pack 1`	— —
Microsoft	Windows 8.1	`x64-based systems` `32-bit systems`	— —
Microsoft	Windows RT 8.1	`Windows RT 8.1`	—
Microsoft	Windows Server 2008	`x64-based Systems Service Pack 2 (Server Core installation)` `32-bit Systems Service Pack 2 (Server Core installation)` `32-bit Systems Service Pack 2` `x64-based Systems Service Pack 2` `Itanium-Based Systems Service Pack 2`	— — — — —
Microsoft	Windows Server 2008 R2	`x64-based Systems Service Pack 1` `Itanium-Based Systems Service Pack 1` `x64-based Systems Service Pack 1 (Server Core installation)`	— — —
Microsoft	Windows Server 2012	`(Server Core installation)`	—
Microsoft	Windows Server 2012 R2	`(Server Core installation)`	—
Microsoft	Windows Server 2016	`(Server Core installation)`	—

Vendors and products

Affected operating systems

Affected operating systems

Windows	microsoft	windows_10_1607	—
Windows	microsoft	windows_10_1703	—
Windows	microsoft	windows_10_1709	—
Windows	microsoft	windows_10_1803	—
Windows	microsoft	windows_7	—
Windows	microsoft	windows_8.1	—
Windows	microsoft	windows_rt_8.1	—
Windows	microsoft	windows_server_2008	`r2`
Windows	microsoft	windows_server_2008	—
Windows	microsoft	windows_server_2012	`r2`
Windows	microsoft	windows_server_2012	—
Windows	microsoft	windows_server_2016	—

Weakness classes (CWE)

CWE-787Out-of-bounds Write
Base
The product writes data past the end, or before the beginning, of the intended buffer.
Entry at MITRE CWE-787

Public exploit references

Publicly reported proof-of-concepts, exploit modules and detection templates for this vulnerability. NEOSEC links to the original sources only and does not provide any exploit code.

Public exploit references

CISA KEV Catalog	CISA Known Exploited Vulnerability (opens in a new tab)cisa.gov	actively exploited	15.02.2022
Exploit-DB	EDB-ID 44741 (opens in a new tab)exploit-db.com	PoC (publicly reported)reported, not verified	—

References & sources

exploit-db.com44741Exploit, x_refsource_EXPLOIT-DB
blog.0patch.com2018/05/a-single-instruction-micropatch-for.htmlx_refsource_MISC
portal.msrc.microsoft.comen-US/security-guidance/advisory/CVE-2018-8174x_refsource_CONFIRM
securityfocus.com103998Vulnerability database, x_refsource_BID
cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2018-8174government-resource

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What is affected, what to do

Metrics

Response and mitigation

Prioritisation rationale

Immediate response (0-24 h)

Mitigation layers

Detection rules

Detection rules

Classification under NIS2 and CRA

Description

Affected products

Vendors and products

Affected operating systems

Weakness classes (CWE)

Public exploit references

References & sources