Microsoft Patch Tuesday — May 2020: Vulnerability disclosures and Snort coverage

A remote code execution vulnerability exists in Microsoft Excel software when the software fails to properly handle objects in memory. An attacker who successfully exploited the vulnerability could run arbitrary code in the context of the current user. If the current user is logged on with administrative user rights, an attacker could take control of the affected system. An attacker could then install programs; view, change, or delete data; or create new accounts with full user rights. Users whose accounts are configured to have fewer user rights on the system could be less impacted than users who operate with administrative user rights. Exploitation of the vulnerability requires that a user open a specially crafted file with an affected version of Microsoft Excel. In an email attack scenario, an attacker could exploit the vulnerability by sending the specially crafted file to the user and convincing the user to open the file. In a web-based attack scenario, an attacker could host a website (or leverage a compromised website that accepts or hosts user-provided content) containing a specially crafted file designed to exploit the vulnerability. An attacker would have no way to force users to visit the website. Instead, an attacker would have to convince users to click a link, typically by way of an enticement in an email or instant message, and then convince them to open the specially crafted file. The security update addresses the vulnerability by correcting how Microsoft Excel handles objects in memory.

A memory corruption vulnerability exists when Windows Media Foundation improperly handles objects in memory. An attacker who successfully exploited the vulnerability could install programs; view, change, or delete data; or create new accounts with full user rights. There are multiple ways an attacker could exploit the vulnerability, such as by convincing a user to open a specially crafted document, or by convincing a user to visit a malicious webpage. The security update addresses the vulnerability by correcting how Windows Media Foundation handles objects in memory.

A remote code execution vulnerability exists in Microsoft SharePoint when the software fails to check the source markup of an application package. An attacker who successfully exploited the vulnerability could run arbitrary code in the context of the SharePoint application pool and the SharePoint server farm account. Exploitation of this vulnerability requires that a user uploads a specially crafted SharePoint application package to an affected version of SharePoint. The security update addresses the vulnerability by correcting how SharePoint checks the source markup of application packages.

A remote code execution vulnerability exists when Internet Explorer improperly accesses objects in memory. The vulnerability could corrupt memory in such a way that an attacker could execute arbitrary code in the context of the current user. An attacker who successfully exploited the vulnerability could gain the same user rights as the current user. If the current user is logged on with administrative user rights, the attacker could take control of an affected system. An attacker could then install programs; view, change, or delete data; or create new accounts with full user rights. An attacker could host a specially crafted website designed to exploit the vulnerability through Internet Explorer and then convince a user to view the website. The attacker could also take advantage of compromised websites, or websites that accept or host user-provided content or advertisements, by adding specially crafted content that could exploit the vulnerability. However, in all cases an attacker would have no way to force a user to view the attacker-controlled content. Instead, an attacker would have to convince a user to take action, typically by an enticement in an email or instant message, or by getting the user to open an attachment sent through email. The security update addresses the vulnerability by modifying how Internet Explorer handles objects in memory.

An elevation of privilege vulnerability exists when Microsoft Edge does not properly enforce cross-domain policies, which could allow an attacker to access information from one domain and inject it into another domain. In a web-based attack scenario, an attacker could host a website that is used to attempt to exploit the vulnerability. In addition, compromised websites and websites that accept or host user-provided content could contain specially crafted content that could exploit the vulnerability. However, in all cases an attacker would have no way to force users to view the attacker-controlled content. Instead, an attacker would have to convince users to take action. For example, an attacker could trick users into clicking a link that takes them to the attacker's site. An attacker who successfully exploited this vulnerability could elevate privileges in affected versions of Microsoft Edge. The security update addresses the vulnerability by helping to ensure that cross-domain policies are properly enforced in Microsoft Edge.

CVE-2020-1054 is an elevation-of-privilege flaw (CWE-787, an out-of-bounds memory access) in the Windows kernel-mode driver (win32k), which fails to properly handle objects in memory. To exploit it, an attacker who can already log on to an affected Windows machine must run a specially crafted application, which triggers the memory-handling error and allows arbitrary code execution in kernel mode. Successful exploitation effectively yields full SYSTEM-level control of the host: the attacker can install programs, view, change or delete any data, and create new accounts with full user rights. Affected products per the CPE data are Windows 7, 8.1, RT 8.1, Windows 10 versions 1507 through 1909, and Windows Server 1803 and 1903. The flaw was fixed in Microsoft's May 2020 Patch Tuesday, a public DrawIconEx-based local privilege escalation PoC exists, EPSS is 54.2% (99th percentile), and CISA added it to the KEV catalog on 2021-11-03, confirming exploitation in the wild; related threat reporting around this CVE ties it to malware campaigns such as PurpleFox and Raspberry Robin, while ransomware use is listed as unknown.

Do: Apply Microsoft's May 2020 security updates (or any later cumulative update) to Windows 7, 8.1, RT 8.1, Windows 10 1507–1909, and Windows Server 1803/1903, per the CISA KEV required action; prioritize multi-user hosts such as RDS servers where low-privileged users can run code. For legacy systems that no longer receive updates (e.g., Windows 7/8.1 post-EOL), limit local logon and software-execution rights for untrusted users and monitor for local privilege escalation activity.

A cross site scripting vulnerability exists when Microsoft Dynamics 365 (on-premises) does not properly sanitize a specially crafted web request to an affected Dynamics server. An authenticated attacker could exploit the vulnerability by sending a specially crafted request to an affected Dynamics server. The attacker who successfully exploited the vulnerability could then perform cross-site scripting attacks on affected systems and run script in the security context of the current authenticated user. These attacks could allow the attacker to read content that the attacker is not authorized to read, use the victim's identity to take actions within Dynamics Server on behalf of the user, such as change permissions and delete content, and inject malicious content in the browser of the user. The security update addresses the vulnerability by helping to ensure that Dynamics Server properly sanitizes web requests.

A remote code execution vulnerability exists in the way that the ChakraCore scripting engine handles objects in memory. The vulnerability could corrupt memory in such a way that an attacker could execute arbitrary code in the context of the current user. An attacker who successfully exploited the vulnerability could gain the same user rights as the current user. If the current user is logged on with administrative user rights, an attacker who successfully exploited the vulnerability could take control of an affected system. An attacker could then install programs; view, change, or delete data; or create new accounts with full user rights. The security update addresses the vulnerability by modifying how the ChakraCore scripting engine handles objects in memory.

An elevation of privilege vulnerability exists in .NET Framework which could allow an attacker to elevate their privilege level. To exploit the vulnerability, an attacker would first have to access the local machine, and then run a malicious program. The update addresses the vulnerability by correcting how .NET Framework activates COM objects.

A denial of service vulnerability exists when .NET Core or .NET Framework improperly handles web requests. An attacker who successfully exploited this vulnerability could cause a denial of service against a .NET Core or .NET Framework web application. The vulnerability can be exploited remotely, without authentication. A remote unauthenticated attacker could exploit this vulnerability by issuing specially crafted requests to the .NET Core or .NET Framework application. The update addresses the vulnerability by correcting how the .NET Core or .NET Framework web application handles web requests.

A memory corruption vulnerability exists when Windows Media Foundation improperly handles objects in memory. An attacker who successfully exploited the vulnerability could install programs; view, change, or delete data; or create new accounts with full user rights. There are multiple ways an attacker could exploit the vulnerability, such as by convincing a user to open a specially crafted document, or by convincing a user to visit a malicious webpage. The security update addresses the vulnerability by correcting how Windows Media Foundation handles objects in memory.

A denial of service vulnerability exists when ASP.NET Core improperly handles web requests. An attacker who successfully exploited this vulnerability could cause a denial of service against an ASP.NET Core web application. The vulnerability can be exploited remotely, without authentication. A remote unauthenticated attacker could exploit this vulnerability by issuing specially crafted requests to the ASP.NET Core application. The update addresses the vulnerability by correcting how the ASP.NET Core web application handles web requests.

A remote code execution vulnerability exists in Visual Studio Code when the Python extension loads configuration files after opening a project. An attacker who successfully exploited the vulnerability could run arbitrary code in the context of the current user. If the current user is logged on with administrative user rights, an attacker could take control of the affected system. An attacker could then install programs; view, change, or delete data; or create new accounts with full user rights. To exploit this vulnerability, an attacker would need to convince a target to clone a repository and open it in Visual Studio Code with the Python extension installed. Attacker-specified code would execute when the target opened the integrated terminal. The update address the vulnerability by modifying the way Visual Studio Code Python extension handles environment variables.

A spoofing vulnerability exists in Microsoft Power BI Report Server in the way it validates the content-type of uploaded attachments. An authenticated attacker could exploit the vulnerability by uploading a specially crafted payload and sending it to the user. The attacker who successfully exploited this vulnerability could then perform actions and run scripts in the security context of the user. This security update addresses the vulnerability by ensuring Power BI Report Server properly validates content-type of the attachments when uploading and opening.