Exploitation evidence
Known exploited · CISA KEV listed
Added 2021-12-15. Ransomware campaign use: Known.
CISA required action: Apply updates per vendor instructions.
CISA due date: 2021-12-29. This is the catalog’s deadline, not an assessment of your organization’s exposure.
KEV checked 13 Nov 2026, 00:20 Jerusalem · Original catalog ↗Reported products and versions
Microsoft / App Installer
Default status: Not specified
- affected: 1.0.0.0 to < publication (custom)
Fixes and workarounds
No explicit solution text in the downloaded CVE record. Consult the vendor advisory; unaffected version ranges are shown above as reported, not inferred as a patch recommendation.
Sources and related reporting
CVE Program record ↗ · Download tracked evidence as JSON
- https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-43890
- https://www.bleepingcomputer.com/news/microsoft/microsoft-disables-msix-protocol-handler-abused-in-malware-attacks/
- https://thehackernews.com/2023/12/microsoft-disables-msix-app-installer.html
- https://www.microsoft.com/en-us/security/blog/2023/12/28/financially-motivated-threat-actors-misusing-app-installer/
- https://github.com/ChrisTitusTech/winutil/pull/26
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-43890
Observed change timeline
History begins when Egret first downloads each source. It is not the complete upstream CVE history.
12 Nov 2026, 18:20 Jerusalem · EPSS observation updated
Stored EPSS snapshot at this observation.
{
"date": "2026-11-12",
"epss": 0.11294,
"percentile": 0.96034
}10 Nov 2026, 18:20 Jerusalem · EPSS observation updated
Stored EPSS snapshot at this observation.
{
"date": "2026-11-10",
"epss": 0.11294,
"percentile": 0.96008
}09 Nov 2026, 18:20 Jerusalem · EPSS observation updated
Stored EPSS snapshot at this observation.
{
"date": "2026-11-09",
"epss": 0.11294,
"percentile": 0.96004
}08 Nov 2026, 18:20 Jerusalem · EPSS observation updated
Stored EPSS snapshot at this observation.
{
"date": "2026-11-08",
"epss": 0.11294,
"percentile": 0.96003
}07 Nov 2026, 18:20 Jerusalem · EPSS observation updated
Stored EPSS snapshot at this observation.
{
"date": "2026-11-07",
"epss": 0.11294,
"percentile": 0.96
}06 Nov 2026, 18:20 Jerusalem · EPSS observation updated
Stored EPSS snapshot at this observation.
{
"date": "2026-11-06",
"epss": 0.11294,
"percentile": 0.95994
}06 Nov 2026, 06:20 Jerusalem · EPSS observation updated
Stored EPSS snapshot at this observation.
{
"date": "2026-11-05",
"epss": 0.11294,
"percentile": 0.9599
}05 Nov 2026, 06:20 Jerusalem · CVE Program record changed
Stored CNA snapshot at this observation.
{
"containers": {
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"url": "https://www.bleepingcomputer.com/news/microsoft/microsoft-disables-msix-protocol-handler-abused-in-malware-attacks/"
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"url": "https://www.microsoft.com/en-us/security/blog/2023/12/28/financially-motivated-threat-actors-misusing-app-installer/"
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"url": "https://github.com/ChrisTitusTech/winutil/pull/26"
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"id": "CVE-2021-43890",
"options": [
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{
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"timestamp": "2021-12-14T00:00:00+00:00",
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"cna": {
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{
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"url": "https://www.bleepingcomputer.com/news/microsoft/microsoft-disables-msix-protocol-handler-abused-in-malware-attacks/"
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{
"url": "https://thehackernews.com/2023/12/microsoft-disables-msix-app-installer.html"
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"url": "https://www.microsoft.com/en-us/security/blog/2023/12/28/financially-motivated-threat-actors-misusing-app-installer/"
},
{
"url": "https://github.com/ChrisTitusTech/winutil/pull/26"
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"datePublished": "2021-12-15T14:15:35.000Z",
"dateReserved": "2021-11-16T00:00:00.000Z",
"dateUpdated": "2026-08-06T03:55:23.978Z",
"state": "PUBLISHED"
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"dataVersion": "5.2"
}04 Nov 2026, 18:20 Jerusalem · EPSS observation updated
Stored EPSS snapshot at this observation.
{
"date": "2026-11-04",
"epss": 0.11294,
"percentile": 0.95988
}03 Nov 2026, 18:20 Jerusalem · EPSS observation updated
Stored EPSS snapshot at this observation.
{
"date": "2026-11-03",
"epss": 0.11294,
"percentile": 0.9598
}03 Nov 2026, 02:22 Jerusalem · EPSS observation updated
Stored EPSS snapshot at this observation.
{
"date": "2026-11-02",
"epss": 0.11294,
"percentile": 0.95975
}03 Nov 2026, 02:22 Jerusalem · CISA KEV status changed
Stored KEV snapshot at this observation.
{
"cveID": "CVE-2021-43890",
"cwes": [],
"dateAdded": "2021-12-15",
"dueDate": "2021-12-29",
"forensicTriage": "No",
"knownRansomwareCampaignUse": "Known",
"notes": "https://nvd.nist.gov/vuln/detail/CVE-2021-43890",
"product": "Windows",
"requiredAction": "Apply updates per vendor instructions.",
"shortDescription": "Microsoft Windows AppX Installer contains a spoofing vulnerability which has a high impacts to confidentiality, integrity, and availability.",
"vendorProject": "Microsoft",
"vulnerabilityName": "Microsoft Windows AppX Installer Spoofing Vulnerability"
}