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CVE-2026-20816 is a local elevation-of-privilege vulnerability in Windows Installer caused by a time-of-check time-of-use (TOCTOU) race condition. The flaw affects the way Windows Installer performs security-sensitive state validation and subsequent use of that state, creating a race window that can be won by a local authorized attacker. Successful exploitation can allow the attacker to elevate privileges on the affected system, with reporting indicating the likely end state is execution with SYSTEM privileges.
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What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.
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.
6 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
Windows Installer elevation of privilege vulnerability assessed as 'Exploitation More Likely' by Microsoft; no exploitation reported in the content.
An elevation-of-privilege vulnerability in Windows Installer that Microsoft assessed as more likely to be exploited.
A local elevation of privilege vulnerability in Windows Installer due to a TOCTOU race condition, potentially allowing SYSTEM-level privilege escalation.
A Windows Installer elevation-of-privilege (EoP) vulnerability that Microsoft rates as more likely to be exploited.
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.