On July 14, 2020 local time, Microsoft addressed a wormable Windows DNS server vulnerability dubbed SigRed (CVE-2020-1350) in its latest monthly patch updates. Once exploited by attackers, the vulnerability could spread between vulnerable computers without user interaction, thereby probably infecting the network of the whole organization.
It is reported that the vulnerability has existed for 17 years and assigns a score of 10 (CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H/E:P/RL:O/RC:C).
When a DNS server parses uploaded queries or responds to forwarded requests, the vulnerability could be exploited.
Check Point researchers found that sending DNS responses containing SIG records (greater than 64 KB) could cause a stack-based buffer overflow, further allowing attackers to control a server.
- Windows Server 2008 for 32-bit Systems Service Pack 2
- Windows Server 2008 for 32-bit Systems Service Pack 2 (Server Core installation)
- Windows Server 2008 for x64-based Systems Service Pack 2
- Windows Server 2008 for x64-based Systems Service Pack 2 (Server Core installation)
- Windows Server 2008 R2 for x64-based Systems Service Pack 1
- Windows Server 2008 R2 for x64-based Systems Service Pack 1 (Server Core installation)
- Windows Server 2012
- Windows Server 2012 (Server Core installation)
- Windows Server 2012 R2
- Windows Server 2012 R2 (Server Core installation)
- Windows Server 2016
- Windows Server 2016 (Server Core installation)
- Windows Server 2019
- Windows Server 2019 (Server Core installation)
- Windows Server, version 1909 (Server Core installation)
- Windows Server, version 1903 (Server Core installation)
- Windows Server, version 2004 (Server Core installation)
Before applying the patches, you are advised to set the maximum length of DNS messages (via TCP) to 0xFF00 to mitigate the vulnerability. This can be achieved by running the following command:
reg add "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\DNS\Parameters" /v "TcpReceivePacketSize" /t REG_DWORD /d 0xFF00 /f
net stop DNS && net start DNS
Meanwhile, you are advised to set the DNS server as the trusted server.
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