Microsoft has released today its monthly batch of security updates, known as Patch Tuesday. This month, the OS maker has fixed 56 security vulnerabilities, including a Windows bug that was being exploited in the wild before today's patches.
Tracked as CVE-2021-1732, the Windows zero-day is an elevation of privelege bug in Win32k, a core component of the Windows operating system.
The bug was exploited after attackers gained access to a Windows system in order to obtain SYSTEM-level access.
According to a report from Chinese security firm DBAPPSecurity, the zero-day was employed by an advanced threat actor known as Bitter, with a long history of attacks targeting Pakistani and Chinese organizations and users.
DBAPPSecurity said the zero-day exploit they initially detected was compiled in May 2020 and was designed to target Windows10 1909 64-bits operating system, but that subsequent tests revealed that the bug also impacted the latest Windows10 20H2 64-bitsOS as well.
Of note was that in its report, the Chinese security firm described the zero-day as "high-quality" and "sophisticated," and said that the attacker used it "with caution," going undetected for almost seven months.
Many bug details went public
Besides the zero-day, this month's Patch Tuesday also stands out because of the high number of vulnerabilities whose details were made public even before patches were available.
In total, six Microsoft product bugs had their details posted online before today's patches. This included:
CVE-2021-1721 - .NET Core and Visual Studio Denial of Service Vulnerability
CVE-2021-1733 - Sysinternals PsExec Elevation of Privilege Vulnerability
"The two RCE vulnerabilities are complex which make it difficult to create functional exploits, so they are not likely [to be exploited] in the short term," Microsoft said in a blog post specifically published to warn about these three issues.
"We believe attackers will be able to create DoS exploits much more quickly and expect all three issues might be exploited with a DoS attack shortly after release," the company added. "Thus, we recommend customers move quickly to apply Windows security updates this month."
Of all Windows systems, Windows Server instances are the ones most likely to be susceptible to attacks, as many are used to host web servers or cloud infrastructure and are almost certainly connected to the internet at all times and exposed to attacks.
"It is essential that customers apply Windows updates to address these vulnerabilities as soon as possible," Microsoft said.
If patches can't be applied right away, various workarounds can be deployed, details in each vulnerability's advisory.
And last but not least, there's also CVE-2021-24078. Described as a remote code execution bug in the Windows DNS server component, the bug could be exploited to hijack domain-name resolution operations inside corporate environments, and redirect legitimate traffic to malicious servers. With a severity score of 9.8 out of 10, the bug is as bad as it gets, if left unpatched, and would most likely atract attackers.
Below are additional details about today's Microsoft Patch Tuesday and security updates released by other tech companies: