CriticalCVE-2024-43573

Windows MSHTML Platform Spoofing Vulnerability (CVE-2024-43573)

Published 08.10.2024In CISA KEV since 08.10.2024Sources: pwn.watch, CVE.org, Msrc Update Guide

Actively exploited

What is affected, what to do

Windows MSHTML Platform Spoofing Vulnerability

The vulnerability is being actively exploited; treat it as a priority. Update Microsoft Windows 10 Version 1507 to version 10.0.10240.20796, Microsoft Windows 10 Version 1607 to version 10.0.14393.7428, Microsoft Windows 10 Version 1809 to version 10.0.17763.6414. Immediate actions, mitigation and detection rules are in the runbook below.

Affected: Microsoft Windows 10 Version 1507 lt 10.0.10240.0..10.0.10240.20796
Microsoft Windows 10 Version 1607 lt 10.0.14393.0..10.0.14393.7428
Microsoft Windows 10 Version 1809 lt 10.0.17763.0..10.0.17763.6414
Microsoft Windows 10 Version 21H2 lt 10.0.19043.0..10.0.19044.5011
Microsoft Windows 10 Version 22H2 lt 10.0.19045.0..10.0.19045.5011
Microsoft Windows 11 version 21H2 lt 10.0.22000.0..10.0.22000.3260
Microsoft Windows 11 version 22H2 lt 10.0.22621.0..10.0.22621.4317
Microsoft Windows 11 version 22H3 lt 10.0.22631.0..10.0.22631.4317
Microsoft Windows 11 Version 23H2 lt 10.0.22631.0..10.0.22631.4317
Microsoft Windows 11 Version 24H2 lt 10.0.26100.0..10.0.26100.2033
Microsoft Windows Server 2012 R2 lt 6.3.9600.0..6.3.9600.22221
Microsoft Windows Server 2012 R2 (Server Core installation) lt 6.3.9600.0..6.3.9600.22221
Microsoft Windows Server 2016 lt 10.0.14393.0..10.0.14393.7428
Microsoft Windows Server 2016 (Server Core installation) lt 10.0.14393.0..10.0.14393.7428
Microsoft Windows Server 2019 lt 10.0.17763.0..10.0.17763.6414
Microsoft Windows Server 2019 (Server Core installation) lt 10.0.17763.0..10.0.17763.6414
Microsoft Windows Server 2022 lt 10.0.20348.0..10.0.20348.2762
Microsoft Windows Server 2022, 23H2 Edition (Server Core installation) lt 10.0.25398.0..10.0.25398.1189
Fixed in: Microsoft Windows 10 Version 1507 10.0.10240.20796
Microsoft Windows 10 Version 1607 10.0.14393.7428
Microsoft Windows 10 Version 1809 10.0.17763.6414
Microsoft Windows 10 Version 21H2 10.0.19044.5011
Microsoft Windows 10 Version 22H2 10.0.19045.5011
Microsoft Windows 11 version 21H2 10.0.22000.3260
Microsoft Windows 11 version 22H2 10.0.22621.4317
Microsoft Windows 11 version 22H3 10.0.22631.4317
Microsoft Windows 11 Version 23H2 10.0.22631.4317
Microsoft Windows 11 Version 24H2 10.0.26100.2033
Microsoft Windows Server 2012 R2 6.3.9600.22221
Microsoft Windows Server 2012 R2 (Server Core installation) 6.3.9600.22221
Microsoft Windows Server 2016 10.0.14393.7428
Microsoft Windows Server 2016 (Server Core installation) 10.0.14393.7428
Microsoft Windows Server 2019 10.0.17763.6414
Microsoft Windows Server 2019 (Server Core installation) 10.0.17763.6414
Microsoft Windows Server 2022 10.0.20348.2762
Microsoft Windows Server 2022, 23H2 Edition (Server Core installation) 10.0.25398.1189

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Metrics

8.1

Priority

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

Source: NVD, CVSS v3

6.5

CVSS v3

Severity Medium on the scale from 0 to 10.

Source: pwn.watch, CVE.org, Msrc Update Guide

46.1 %

EPSS score

Elevated — model estimates 10-50% exploitation likelihood.

Source: FIRST EPSS, percentile 98.8

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: 217.02 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: 8.1 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: 6.5
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: 46.1 %; Elevated — model estimates 10-50% exploitation likelihood.
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: 98.8; 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: 08.10.2024
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: 08.10.2024
CISA assessment (SSVC): Exploitation: active · not automatable · Technical impact: partial; Source: CISA Vulnrichment, as of 9 October 2024
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-79

Response and mitigation

Why act now?

Prioritisation rationale

The flaw is network-reachable without authentication but requires user interaction. It belongs to the family of MSHTML spoofing bugs where the long-retired Internet Explorer engine is revived through crafted shortcuts to fool security prompts and disguise malicious payloads as benign documents. Attackers typically weaponise it in phishing campaigns against knowledge workers and back-office staff. Exploitation likelihood is very high, and CISA has not flagged ransomware use. For organisations with a large Windows client estate and meaningful email exposure, treat this as critical with a 7-day patch SLA. Server-only or OT environments without interactive users can rank it lower, but should still fast-track administrator workstations.

01
Runbook step 1
Immediate response (0-24 h)
- Deploy the October 2024 security updates (Patch Tuesday, 2024-10-08) to all Windows clients. Target builds per context: Windows 10 1507 ≥ 10.0.10240.20796, 1607 ≥ 10.0.14393.7428, 1809 ≥ 10.0.17763.6414, 21H2 ≥ 10.0.19044.5011, 22H2 ≥ 10.0.19045.5011; Windows 11 21H2 ≥ 10.0.22000.3260, 22H2 ≥ 10.0.22621.4317, 23H2/"22H3" ≥ 10.0.22631.4317. Look up the per-build KB numbers in the Microsoft Security Update Guide. Windows Server SKUs are not listed in the context — confirm their exposure in the vendor advisory.
- Reconcile patch state against those build numbers via your inventory tooling (Intune, SCCM/MECM, WSUS or Defender Vulnerability Management). Fix unpatched endpoints used by privileged staff first: admins, finance and executives.
- Tighten the mail gateway now: quarantine attachments with .url, .lnk, .hta, .mht or .mhtml extensions. Also quarantine archives (ZIP/RAR/ISO) that contain them. These file types are the usual carriers for MSHTML spoofing chains.
- Push a short user advisory through awareness channels. Tell users not to open internet shortcuts or "PDF" files from archives that trigger an Internet Explorer window or a security prompt.
- Start a retro-hunt (see Detection rules) covering at least 30 days before 2024-10-08 up to today. Treat any hit as an incident: isolate the host and reset the user's credentials. Confidentiality loss is the primary impact.
02
Runbook step 2
Mitigation layers
- Endpoint hardening: Enable the Defender ASR rules "Block execution of potentially obfuscated scripts" and "Block Office/communication apps from creating executable content" in block mode. Restrict mshta.exe for standard users via AppLocker or WDAC.
- Legacy browser configuration: Disable Edge IE mode via GPO or Intune where there is no hard business need. Where IE mode is required, restrict it to an explicit site list. Also enforce the GPO "Disable Internet Explorer 11 as a standalone browser".
- Mark-of-the-Web / SmartScreen: Set SmartScreen for Explorer and Edge to block. Make sure archive tools propagate MotW to extracted files (7-Zip zone-ID propagation, WinRAR).
- Network: Log outbound connections from iexplore.exe at the proxy and restrict them to an allowlist. Block .hta and .mht downloads from the internet zone at the secure web gateway.
- IAM/least privilege: Remove local admin rights from workstations (LAPS / Windows LAPS). This limits follow-on execution once a user has been deceived.
- Mail security: Add a rule for attachment names with double extensions or long runs of whitespace or Braille-blank padding before the real extension (e.g. Invoice.pdf .hta). This disguise technique is known from comparable MSHTML spoofing cases.
03
Runbook step 3
Detection rules
- Sysmon EID 1 / Security EID 4688: iexplore.exe with a command line containing mhtml: or !x-usc:, parent explorer.exe. KQL: DeviceProcessEvents | where FileName =~ "iexplore.exe" and ProcessCommandLine has_any ("mhtml:", "x-usc:")
- EDR process ancestry: iexplore.exe or msedge.exe (IE mode) spawning mshta.exe, cmd.exe, powershell.exe, wscript.exe or rundll32.exe. Sigma shape: ParentImage|endswith: '\iexplore.exe' AND Image|endswith: ['\mshta.exe','\powershell.exe','\cmd.exe','\wscript.exe'].
- Sysmon EID 11 (FileCreate): .url files dropped into \Downloads\, \AppData\Local\Temp\ or Outlook cache paths. Follow up with a content sweep (EDR live response or YARA) for lines such as URL=mhtml: or IconFile= pointing to UNC or HTTP paths.
- Proxy/Zeek HTTP: User-Agent containing MSIE or Trident/7.0 from workstations that normally only run Edge or Chrome. Also watch for downloads with MIME type application/hta or message/rfc822 from the internet zone. SPL: index=proxy (useragent="*Trident/7.0*" OR content_type="application/hta") | stats count by src_ip, url
- Defender telemetry: SmartScreen or MotW warnings that the user overrode (DeviceEvents, ActionType SmartScreenUserOverride).

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

Windows MSHTML Platform Spoofing Vulnerability

Source: pwn.watch, NVD (NIST), Microsoft Security Update Guide, CISA KEV Catalog, CVE.org (MITRE), cvelistv5

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 Version 1507	`10.0.10240.0 – < 10.0.10240.20796`	`10.0.10240.20796`
Microsoft	Windows 10 Version 1607	`10.0.14393.0 – < 10.0.14393.7428`	`10.0.14393.7428`
Microsoft	Windows 10 Version 1809	`10.0.17763.0 – < 10.0.17763.6414`	`10.0.17763.6414`
Microsoft	Windows 10 Version 21H2	`10.0.19043.0 – < 10.0.19044.5011`	`10.0.19044.5011`
Microsoft	Windows 10 Version 22H2	`10.0.19045.0 – < 10.0.19045.5011`	`10.0.19045.5011`
Microsoft	Windows 11 version 21H2	`10.0.22000.0 – < 10.0.22000.3260`	`10.0.22000.3260`
Microsoft	Windows 11 version 22H2	`10.0.22621.0 – < 10.0.22621.4317`	`10.0.22621.4317`
Microsoft	Windows 11 version 22H3	`10.0.22631.0 – < 10.0.22631.4317`	`10.0.22631.4317`
Microsoft	Windows 11 Version 23H2	`10.0.22631.0 – < 10.0.22631.4317`	`10.0.22631.4317`
Microsoft	Windows 11 Version 24H2	`10.0.26100.0 – < 10.0.26100.2033`	`10.0.26100.2033`
Microsoft	Windows Server 2012 R2	`6.3.9600.0 – < 6.3.9600.22221`	`6.3.9600.22221`
Microsoft	Windows Server 2012 R2 (Server Core installation)	`6.3.9600.0 – < 6.3.9600.22221`	`6.3.9600.22221`
Microsoft	Windows Server 2016	`10.0.14393.0 – < 10.0.14393.7428`	`10.0.14393.7428`
Microsoft	Windows Server 2016 (Server Core installation)	`10.0.14393.0 – < 10.0.14393.7428`	`10.0.14393.7428`
Microsoft	Windows Server 2019	`10.0.17763.0 – < 10.0.17763.6414`	`10.0.17763.6414`
Microsoft	Windows Server 2019 (Server Core installation)	`10.0.17763.0 – < 10.0.17763.6414`	`10.0.17763.6414`
Microsoft	Windows Server 2022	`10.0.20348.0 – < 10.0.20348.2762`	`10.0.20348.2762`
Microsoft	Windows Server 2022, 23H2 Edition (Server Core installation)	`10.0.25398.0 – < 10.0.25398.1189`	`10.0.25398.1189`

Vendors and products

Affected operating systems

Affected operating systems

Windows	microsoft	windows_10_1507	—
Windows	microsoft	windows_10_1607	—
Windows	microsoft	windows_10_1809	—
Windows	microsoft	windows_10_21h2	—
Windows	microsoft	windows_10_22h2	—
Windows	microsoft	windows_11_21h2	—
Windows	microsoft	windows_11_22h2	—
Windows	microsoft	windows_11_23h2	—
Windows	microsoft	windows_11_24h2	—
Windows	microsoft	windows_server_2012	`r2`
Windows	microsoft	windows_server_2016	—
Windows	microsoft	windows_server_2019	—
Windows	microsoft	windows_server_2022	—
Windows	microsoft	windows_server_2022_23h2	—

Weakness classes (CWE)

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
Base
The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.
Entry at MITRE CWE-79

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	08.10.2024

References & sources

Microsoft Security Update GuideWindows MSHTML Platform Spoofing VulnerabilityVendor advisory, Patch, Patch, Vendor advisory, pwn-watch
cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2024-43573government-resource, US government resource
pwn.watchpwn.watch: Microsoft October 2024: 2 actively exploited zero-dayspwn-watch
Microsoft Security Update GuideMicrosoft advisory: CVE-2024-43572pwn-watch
NVD (NIST)NVD: CVE-2024-43572pwn-watch
NVD (NIST)NVD: CVE-2024-43573pwn-watch
cisa.govCISA Known Exploited Vulnerabilities Catalogpwn-watch

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<a href="https://intel.neosec.eu/en/cve/CVE-2024-43573"><img src="https://intel.neosec.eu/badge/cve/CVE-2024-43573.svg?lang=en" alt="CVE-2024-43573 – NEOSEC Intel" height="20"></a>

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