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CVE-2021-43890 is a spoofing vulnerability in Microsoft Windows AppX/App Installer. The issue allows specially crafted application installation packages, including packages invoked through the ms-appinstaller URI scheme, to misrepresent publisher identity and trusted branding during installation. Observed abuse showed malicious App Installer packages presenting themselves as legitimate software while the displayed publisher information did not reliably reflect the actual signing identity, enabling attackers to socially engineer users into approving installation of malware-laden MSIX/AppX content. Microsoft assigned this CVE to the App Installer process issue and fixed it in the January 2022 Patch Tuesday release. The vulnerability has been used in phishing and malware-delivery campaigns involving families such as Emotet, TrickBot, and BazarLoader, and later abuse of the ms-appinstaller protocol led Microsoft to disable that protocol by default in newer App Installer builds.
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What an attacker gets, and what they’ve been doing with it.
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Patch, then assume compromise.
No public exploits tracked yet. Mallory keeps watching.
No public exploit code observed for this vulnerability.
Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.
Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.
7 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
A Microsoft vulnerability that CISA KEV’s knownRansomwareCampaignUse field silently flipped to Known during 2025 (evidence of ransomware campaign use).
A Windows App Installer process vulnerability abused to deliver malware via ms-appinstaller links and malicious .appinstaller/.appxbundle packages, enabling deceptive installation of BazarBackdoor/BazarLoader payloads.
Unknown (the content only lists this CVE as a reference and does not describe the vulnerability, impact, affected products, or exploitation details).
A spoofing vulnerability in the Windows AppX Installer.
Query your assets running an affected version, and investigate the blast radius.
Every observed campaign linking this CVE to a named adversary.
Malware families riding this exploit, with evidence and IOCs.
YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.
Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.