CVE-2021-42278
HIGHCVE-2021-42278 is a high-severity (CVSS 7.5) vulnerability in microsoft windows server 20h2. It is in CISA's Known Exploited Vulnerabilities catalog (added 2022-04-11) and has been used in ransomware campaigns — treat it as actively exploited and patch now. O3 Security detects and blocks CVE-2021-42278 exploitation at runtime via eBPF exploit-chain detection and L7 egress monitoring, even on unpatched systems.
Active Directory Domain Services Elevation of Privilege Vulnerability
Exploitation Status
Actively exploited in the wild
- Confirmed by CISA's Known Exploited Vulnerabilities catalog on 2022-04-11 — including use in ransomware campaigns. Federal agencies were required to remediate by 2022-05-02.
- A successful exploit gives an attacker total control of the affected component, not partial access.
Exploitation and automatability from CISA (KEV catalog and SSVC triage) for CVE-2021-42278.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2021-42278 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE sits: patch-first territory.
Where this sits among everything scored
Of 0 CVEs with a current EPSS score, this one falls in the 50–90% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Description
Active Directory Domain Services Elevation of Privilege Vulnerability
Affected Products
windows server 20h2microsoftwindows server 2004microsoftwindows server 2008microsoftwindows server 2012microsoftwindows server 2016microsoftwindows server 2019microsoftResearch use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Active Directory Domain Services Elevation of Privilege Vulnerability
Active Directory Domain Services Elevation of Privilege Vulnerability
Active Directory Domain Services Elevation of Privilege Vulnerability
Active Directory Domain Services Elevation of Privilege Vulnerability
Active Directory Domain Services Elevation of Privilege Vulnerability
Active Directory Domain Services Elevation of Privilege Vulnerability
Active Directory Domain Services Elevation of Privilege Vulnerability
Active Directory Domain Services Elevation of Privilege Vulnerability
Detection & mitigation playbook
Vendor / applianceDetect
Inventory every microsoft windows server 20h2 deployment and check each version against the affected-products list above. Because the exploit targets the running system rather than your application code, also watch for exploitation at the network and runtime layer — O3 flags the exploit behaviour from runtime telemetry and egress traffic even before a vulnerable build is confirmed.
Fix
Apply the microsoft windows server 20h2 security patch or hotfix for CVE-2021-42278 on the affected version, following the vendor advisory for your exact build.
Workarounds
Cut exposure now: restrict the management/admin interface to trusted networks, segment the device, and apply the vendor's recommended configuration mitigations and any WAF/IPS signature. O3's runtime protection blocks the exploit chain at execution, holding the line on unpatched or end-of-life systems until you can patch.
How O3 protects you
O3 detects and blocks CVE-2021-42278 exploitation at runtime: eBPF exploit-chain detection, plus L7 egress monitoring that catches the post-exploitation callback and severs the attacker's outbound channel.
Tailored to CVE-2021-42278. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2021-42278 being exploited in your environment?
O3's eBPF runtime sensors and L7 egress monitoring detect and block the CVE-2021-42278 exploit chain at execution — protecting unpatched and end-of-life systems until the vendor patch is applied.