CVE-2021-43890
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Windows AppX Installer Spoofing Vulnerability
rank 69 = 40 + 18 + 1 + 4 + 6
rank@v1 · this cycle
Someone is already using it
CISA KEV catalog · public proof-of-concept · FIRST EPSS
EPSS 0.10295 · CISA KEV listed · without this subject the record ranks 29
What it costs you if it fires
NVD CVSS base score, then the CNA's own
CVSS 7.1, from NVD · without this subject the record ranks 51
It is getting worse, not staying still
FIRST EPSS series, rescorings and bad loads removed
rose on 2026-05-08 · without this subject the record ranks 68
How much of the world it touches
NVD CPE configurations
2 products in the CPE ranges · without this subject the record ranks 65
Someone else already set the date
CISA KEV remediation due date
CISA remediation date held · without this subject the record ranks 63
$514,000 = $4.99M incident cost x 1 exposure x 0.10295 likelihood
udv@v1 · unaudited · wrong for you until you say what you run
$4.99M is the cost of a breach that happened, from IBM Cost of a Data Breach Report 2026, global average. It is not the value of any asset of yours. That average already covers breaches of every severity, so scaling it by exposure understates a partial-impact record. That is an assumption, not a measurement. Your own asset value goes in the decision record.
Hindsight · the state
Foresight · where to check next
No weakness class or product neighbourhood is held for this record, so this index cannot name anywhere to check next. That is an absence in the record, not a finding about the software.
Running Microsoft App Installer? Check your version
A deterministic range check against the ranges this record publishes. It tells you where a version sits in the record, not whether your deployment is exploitable. No account needed.
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Harm, if it fires from the vector and the weakness
Written for the ticket you're about to file.
CISA KEV & Federal Remediation Deadline from the record and CISA
The fix, and how long it's been waiting.
Exploit Status & Known PoCs a ladder, not a score
Current rung: Ransomware campaign use known, 2021-12-15.
A rung lights from a row in the index, never from an assessment. "Held sources" is the true scope of the claim: this index reads the CVE record, NVD, CISA KEV, FIRST's EPSS and public proof-of-concept repositories, and it does not observe attacks.
What it is stated by the CNA
We have investigated reports of a spoofing vulnerability in AppX installer that affects Microsoft Windows. Microsoft is aware of attacks that attempt to exploit this vulnerability by using specially crafted packages that include the malware family known as Emotet/Trickbot/Bazaloader. An attacker could craft a malicious attachment to be used in phishing campaigns. The attacker would then have to convince the user to open the specially crafted attachment. Users whose accounts are configured to have fewer user rights on the system could be less impacted than users who operate with administrative user rights. Please see the Security Updates table for the link to the updated app. receipt
Read the rest of the CNA's description
Alternatively you can download and install the Installer using the links provided in the FAQ section. Please see the Mitigations and Workaround sections for important information about steps you can take to protect your system from this vulnerability. December 27 2023 Update: In recent months, Microsoft Threat Intelligence has seen an increase in activity from threat actors leveraging social engineering and phishing techniques to target Windows OS users and utilizing the ms-appinstaller URI scheme. To address this increase in activity, we have updated the App Installer to disable the ms-appinstaller protocol by default and recommend other potential mitigations.
NVD's analysis a second authority
- severity
- 7.1 CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:H/I:H/A:H
- affected versions
- microsoft app installer < 1.16; microsoft app installer < 1.11
- also scored by
- [email protected] 7.1 CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:H/I:H/A:H
check it yourself portal.msrc.microsoft.com bleepingcomputer.com thehackernews.com microsoft.com github.com receipt
Dated events
Movement the material steps
Show all 37 observations
37 observations held. A highlighted step crossed a promotion threshold. A step marked with a scoring model moved because the instrument was replaced, not because the vulnerability changed. receipt
The full biography
Listed by CISA on the day it published and the record had been public for 4 years, 8 months when this index was last written.
No material movement in 81 days as of the last ingest this index recorded.
Siblings and hubs
Records related to this one
None. No alias set, and nothing in the corpus cites this identifier or shares its product family within 60 days.
Browse the index from here
These are index-wide views, not findings about CVE-2021-43890.
What usually comes next
Everything above needs no account. What is below is work: assembling it, scoping it to your estate, watching it, and handing it to someone else.