Cybersecurity Briefing — SMBv3 remote code execution (CVE-2020-0796)
Microsoft rushed an out-of-band fix for CVE-2020-0796 on March 12, 2020, correcting an SMBv3 compression flaw affecting Windows 10 and Server 1903/1909. The pre-auth remote code execution risk on standard SMB ports required rapid patching and network mitigation to block wormable spread.
Executive briefing: Microsoft released an out-of-band patch for CVE-2020-0796 on . The SMBv3 compression flaw let unauthenticated attackers execute code on clients and servers running Windows 10 version 1903/1909 and corresponding Windows Server builds.
Why it matters
- Pre-auth exploitation: no credentials required, exposing file servers and workstations reachable on TCP 445.
- Wormable potential: similar to WannaCry vectors, unpatched networks risk automated lateral movement.
- Client impact: Windows 10 endpoints opening malicious SMB shares could be compromised even without hosting shares.
Operator actions
- Patch now: Deploy the March 12 cumulative update to all affected Windows 10 and Server 1903/1909 systems.
- Network containment: Block inbound SMB (TCP 445) from the internet and segment internal SMB traffic where possible.
- Disable compression: Apply the PowerShell workaround from ADV200005 on systems that cannot be patched immediately.
- Monitor telemetry: Hunt for connections to unknown SMB servers and scan endpoints for post-exploitation tooling.
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