High
CVE-2021-26897
CVE-2021-26897
Add Assessment
Technical Analysis
Vulnerability Overview
0patch released a blog article about their micro patch concerning CVE-2021-26897. It describes the root cause as
CVE-2021-26897 is a buffer overflow issue, whereby a series of oversized “dynamic update” DNS queries with SIG (signature) records causes writing beyond the buffer boundary when these records are saved to file.
According to the blog article the record saves happen
- periodically or
- when the DNS service stops
The analysis of 0patch was based on an article from the McAfee Labs. They provided enough information to enable 0patch to gain understanding were the vulnerability is located.
Successful exploitation of this vulnerability results in running code with Local System privileges. A attacker does need a domain joined computer and have access to a DNS server. The configuration of the DNS server needs to have Dynamic Updates activated.
In an Active Directory environment Dynamic Updates are enabled by default. The default setting secure dynamic updates only allows domain joined computers to update a DNS zone.
Score reasoning
I rated the Attack Value pretty high. Successful exploitation provides adversaries with high privileged access to domain controllers.
The Exploitability score is based on the fact, that the vulnerability can be reversed through public resources and seems to be a buffer overflow. Nevertheless the broader mass of adversaries might be waiting for a detailed writeup or P-o-C and act opportunistic.
Sources:
CVSS V3 Severity and Metrics
General Information
Vendors
- microsoft
Products
- windows server 2008 r2,
- windows server 2008 sp2,
- windows server 2012 -,
- windows server 2012 r2,
- windows server 2016 -,
- windows server 2016 1909,
- windows server 2016 2004,
- windows server 2016 20h2,
- windows server 2019 -
