Cybersecurity Briefing — Exchange Server patch for CVE-2020-0688
Microsoft's February 2020 Patch Tuesday fixed CVE-2020-0688, a remote code execution flaw in Exchange Server caused by a static cryptographic key in the Control Panel. Servers left unpatched or without reset Exchange Control Panel machine keys remained trivially exploitable by authenticated attackers.
Executive briefing: Microsoft addressed CVE-2020-0688 during . The flaw reused a static key for deserializing Exchange Control Panel data, letting any authenticated mailbox user execute code on the underlying Windows server. Unpatched Internet-facing Exchange servers were widely scanned within days of release.
Why it matters
- Compromise path: an attacker with any valid mailbox credentials could achieve system-level code execution without multi-factor gaps or social engineering.
- Exposure: Exchange Control Panel is commonly published through Outlook Web Access, so vulnerable deployments were directly reachable from the internet.
- Persistence: Attackers dropping web shells on unpatched servers enable long-term tenant access and data exfiltration.
Operator actions
- Patch priority: Verify all supported Exchange 2010, 2013, 2016, and 2019 servers have February 11, 2020 security updates installed.
- Reset keys: Follow ADV200006 to regenerate Exchange Control Panel machine keys after patching to invalidate serialized viewstate.
- Investigate compromise: Hunt for anomalous ECP logins and web shell drops under
C:\Program Files\Microsoft\Exchange Server\V15\FrontEnd\HttpProxy\owa\auth\. - Harden exposure: Require MFA for all remote Exchange services and limit ECP access to administrative networks.
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