On October 13, 2020 (local time), Microsoft fixed a critical vulnerability dubbed Bad Neighbor (CVE-2020-16898) in the Windows TCP/IP stack in its latest monthly patch update. An attacker might execute arbitrary code on a remote system by sending maliciously crafted ICMPv6 Router Advertisement packets.
McAfee said the proof-of-concept code shared with MAPP (Microsoft Active Protection Program) members is both simple and reliable and can result in an immediate BSOD (Blue Screen of Death)
According to Microsoft, the CVSS base score of this vulnerability is 9.8: (CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H/E:P/RL:O/RC:C).
A vulnerability exists when the Windows TCP/IP stack improperly handles ICMPv6 Router Advertisement packets that use Option Type 25 (Recursive DNS Server Option) and a length field value that is even.
When an even length value is provided, the Windows TCP/IP stack incorrectly advances the network buffer by an amount that is 8 bytes too few. This is because the stack internally counts in 16-byte increments, failing to account for the case where a non-RFC compliant length value is used. This mismatch results in the stack interpreting the last 8 bytes of the current option as the start of a second option, ultimately leading to a buffer overflow and potential RCE.
- Windows 10 Version 1709 for 32-bit Systems
- Windows 10 Version 1709 for ARM64-based Systems
- Windows 10 Version 1709 for x64-based Systems
- Windows 10 Version 1803 for 32-bit Systems
- Windows 10 Version 1803 for ARM64-based Systems
- Windows 10 Version 1803 for x64-based Systems
- Windows 10 Version 1809 for 32-bit Systems
- Windows 10 Version 1809 for ARM64-based Systems
- Windows 10 Version 1809 for x64-based Systems
- Windows 10 Version 1903 for 32-bit Systems
- Windows 10 Version 1903 for ARM64-based Systems
- Windows 10 Version 1903 for x64-based Systems
- Windows 10 Version 1909 for 32-bit Systems
- Windows 10 Version 1909 for ARM64-based Systems
- Windows 10 Version 1909 for x64-based Systems
- Windows 10 Version 2004 for 32-bit Systems
- Windows 10 Version 2004 for ARM64-based Systems
- Windows 10 Version 2004 for x64-based Systems
- Windows Server 2019
- Windows Server 2019 (Server Core installation)
- Windows Server, version 1903 (Server Core installation)
- Windows Server, version 1909 (Server Core installation)
- Windows Server, version 2004 (Server Core installation)
Microsoft has released security patches for vulnerable systems. Affected users are strongly advised to install patch updates as soon as possible. For patch updates, please visit the following link:
Besides, it has provided the following mitigations:
- Disable ICMPv6 RDNSS
You can disable ICMPv6 RDNSS, to prevent attackers from exploiting the vulnerability, with the following PowerShell command. This workaround is only available for Windows 1709 and above.
Note: No reboot is needed after making the change.
You can disable the workaround with the following command:
Note: No reboot is needed after disabling the workaround.
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