One of the vulnerabilities that Microsoft addressed as part of the October 2020 Patch Tuesday is a critical bug in Windows’ TCP/IP driver that could lead to the remote execution of code.
Tracked as CVE-2020-16898, the issue is triggered when the TCP/IP stack doesn’t handle ICMPv6 Router Advertisement packets properly. An attacker could send specially crafted ICMPv6 Router Advertisement packets to a remote Windows machine to exploit the flaw and execute arbitrary code, Microsoft explains.
The tech company notes that Windows 10 and Windows Server are vulnerable to attacks and that there are no mitigations. However, one workaround is available.
A second issue in the TCP/IP driver, which is tracked as CVE-2020-16899, could be exploited to cause the target computer to stop responding. This flaw too can be exploited through crafted packets, but would not result in code execution, Microsoft says. The company rated the flaw as important.
SophosLabs’ security researchers have published a video to demonstrate how the first vulnerability (CVE-2020-16898) can be exploited to trigger a Blue Screen of Death (BSoD). They described it as a so-called “Ping of Death” vulnerability.
The issue, they say, resides in the tcpip.sys kernel driver and is caused by a logic error in how ICMP (Internet Control Message Protocol) messages are parsed. To trigger the flaw, an attacker would need to send “a crafted IPv6 router advertisement packet containing a Recursive DNS Server (RDNSS) option.”
The packet, they explain, would contain more data than expected, thus resulting in the driver “putting more bytes of data on its memory stack than provided for in the driver’s code, resulting in a buffer overflow.”
While both denial of service and remote code execution are possible by exploiting the bug, in practice, the latter would be extremely difficult to achieve, the researchers say. SophosLabs’ researchers created proof-of-concept (PoC) code to exploit the issue but won’t release details on it yet, to prevent exploitation.
“Once we understood the bug, developing a ‘Blue Screen of Death’ proof-of-concept was fairly straightforward. But taking it to the level that Microsoft has warned is possible—remote code execution (RCE)—is not. Modern defensive coding standards and practices would slow down an effort to build a reliable generic RCE exploit, for two reasons,” SophosLabs notes.
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