Microsoft Patch Tuesday: 83 Vulnerabilities, 10 Critical, 1 Actively Exploited

Microsoft on Tuesday released the first batch of security patches for 2021 with fixes for 83 documented security vulnerabilities, including a “critical” bug in the Defender security product that’s being actively exploited.

Security experts are urging security response personnel to pay special attention to CVE-2021-1647, which describes a remote code execution flaw in Microsoft Defender, the company’s flagship anti-malware product.

The Microsoft Defender update comes with an “exploitation detected” warning and was shipped via the Microsoft Malware Protection Engine, a utility used to clean-up remnants of known malware attacks.

“Best practices recommend that customers regularly verify whether software distribution, such as the automatic deployment of Microsoft Malware Protection Engine updates and malware definitions, is working as expected in their environment,” the company urged.

Microsoft did not provide details on the active attacks.

Of the 83 vulnerabilities documented for January, 10 are rated “critical,” Microsoft’s highest severity rating.   The remainder are slated as “important” because of the risk of code execution, information disclosure or denial-of-service attacks.

The January batch of patches cover serious security holes in Microsoft Office, Microsoft Office Services and Web Apps, Microsoft WIndows, Visual Studio, .Net Core and Azure.

According to Dustin Childs, a research who tracks security updates for ZDI, the major bug in the Microsoft Malware Protection Engine may already be patched as the engine auto-updates as needed. “However, if your systems are not connected to the Internet, you’ll need to manually apply the patch,” Childs said in a blog post.

He also called attention to the following bulletins:

CVE-2021-1648 – Microsoft splwow64 Elevation of Privilege Vulnerability: This bug was publicly disclosed by ZDI after it exceeded our disclosure timeline. It was also discovered by Google, likely because this patch corrects a bug introduced by a previous patch. The previous patch introduced a function to check an input string pointer, but in doing so, it introduced an Out-of-Bounds (OOB) Read condition. Additional bugs are also covered by this patch, including an untrusted pointer deref. The previous CVE was being exploited in the wild, so it’s within reason to think this CVE will be actively exploited as well.

CVE-2021-1677 – Azure Active Directory Pod Identity Spoofing Vulnerability: This vulnerability exists in the way that the Azure Active Directory (AAD) pod identity allows users to assign identities to pods in Kubernetes clusters. When an identity is assigned to a pod, the pod can access to the Azure Instance Metadata Service (IMDS) endpoint and get a token of that identity. This could allow an attacker to laterally steal the identities that are associated with different pods. This is also requires more than just a patch to fix. Anyone with an existing installation will need to re-deploy their cluster and use Azure CNI instead of the default Kubernetes.

CVE-2021-1674 – Windows Remote Desktop Protocol Core Security Feature Bypass Vulnerability: This patch is a bit of a mystery. It carries a relatively high CVSS score (8.8), but without an executive summary, we can only guess what security feature in RDP Core is being bypassed. Short of reversing the patches, we don’t even know how this is different than CVE-2021-1669 – Windows Remote Desktop Security Feature Bypass Vulnerability. What we do know is that RDP has been a popular target in recent memory, and these bugs should be taken seriously. Without any solid information to act on, defenders should assume the worst-case scenario and restrict access to RDP wherever possible.  

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