CVE-2020-1350

CVE-2020-1350 is a critical (CVSS 10.0) remote code execution vulnerability in the DNS Server role of Microsoft Windows Server, caused by improper input handling (CWE-20) when the server fails to properly process crafted DNS requests, notably malicious DNS signature (SIG) records delivered over TCP. An unauthenticated attacker can trigger it by sending a crafted DNS query that forces the vulnerable DNS server to perform an upstream lookup and receive a malicious response, overflowing a heap buffer. Successful exploitation yields code execution with SYSTEM privileges on the DNS server, which is very often an Active Directory domain controller, giving the attacker control of the host and typically the entire domain; the flaw is considered wormable because compromised DNS servers can propagate attacks to other servers they query. Any Windows Server 2008, 2012, 2016, or 2019 host running the DNS Server role is affected — internet-facing DNS servers are directly explovable, while internal DNS servers can be reached via malicious DNS responses passed through firewalls. The flaw was fixed in Microsoft's July 2020 updates, is listed in CISA's Known Exploited Vulnerabilities catalog (added 2021-11-03, required action: apply vendor updates), carries EPSS of 91.4% (100th percentile), and appears in the NSA's top-25 list of flaws exploited by Chinese state-sponsored hackers; no public PoC is cataloged in this dataset and ransomware use is listed as unknown.

What to do: Apply the July 2020 (or later) Microsoft security updates for each affected Windows Server release, prioritizing internet-facing DNS servers and domain controllers; if patching must be delayed, apply Microsoft's registry-based workaround limiting TCP DNS packet size (TcpReceivePacketSize = 0xFF00) and restart the DNS Server service. Inventory hosts with the DNS Server role installed and review their TCP/53 exposure, especially any resolvers reachable from the internet, and confirm remediation per CISA's required action.