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Patch now! VMWare escape flaws are so serious even end-of-life software gets a fix

VMWare has issued secuity fixes for its VMware ESXi, Workstation, Fusion, and Cloud Foundation products. It has even taken the unusual step of issuing updates for versions of the affected software that have reached thier end-of-life, meaning they would normally no longer be supported.

This flaws affect customers who have deployed VMware Workstation, VMware Fusion, and/or VMware ESXi by itself or as part of VMware vSphere or VMware Cloud Foundation.

A virtual machine (VM) is a computer program that emulates a physical computer. A physical “host” computer can run multiple separate “guest” VMs that are isolated from each other, and from the host. The physical resources of the host are allocated to the VMs by a software layer called the hypervisor, which acts an intermediary between the host and the VM (the guest system).

VMWare’s decision to offer fixes for end-of-life software is because the vulnerabilities patched in these updates are escape flaws that allow a computer program to breack of the confines of a VM and affect the host operating system. Specifically, an attacker with privileged access, such as root or administrator, on a guest VM can access the hypervisor on the host.

Besides instructions about how to update the affected products, the advisory lists possible workarounds that would block an attacker from exploiting the vulnerabilities. Since three of the vulnerabilities affect the USB controller, applying the workarounds will effectively block the use of virtual or emulated USB devices. For guest operating systems that do not support using a PS/2 mouse and keyboard, such as macOS, this means they will effectively be unable to use a mouse and keyboard.

The Common Vulnerabilities and Exposures (CVE) database lists publicly disclosed computer security flaws. The CVEs patched in these updates are:

CVE-2024-22252 and CVE-2024-22253 are use-after-free vulnerabilities in the XHCI and UHCI USB controllers of VMware ESXi, Workstation, and Fusion. A malicious actor with local administrative privileges on a virtual machine can exploit the issues to execute code as the virtual machine’s VMX process running on the host. On ESXi, the exploitation of either is contained within the VMX sandbox, but on Workstation and Fusion this may lead to code execution on the machine where Workstation or Fusion is installed.

The VMX process is a process that runs in the kernel of the VM and is responsible for handling input/output (I/O) to devices that are not critical to performance. The VMX is also responsible for communicating with user interfaces, snapshot managers, and remote consoles.

Use-after-free vulnerabilities are the result of the incorrect use of dynamic memory during a program’s operation. If, after freeing a memory location, a program does not clear the pointer to that memory, an attacker can exploit the error to manipulate the program. Referencing memory after it has been freed can cause a program to crash, use unexpected values, or execute code.

CVE-2024-22254 is an out-of-bounds write vulnerability in VMWare ESXi. A malicious actor with privileges within the VMX process can trigger an out-of-bounds write leading to an escape of the sandbox.

A sandbox environment is another name for an isolated VM in which potentially unsafe software code can execute without affecting network resources or local applications.

An out-of-bounds write can occur when a program writes outside the bounds of an allocated area of memory, potentially leading to a crash or arbitrary code execution. This can happen when the size of the data being written to memory is larger than the size of the allocated memory area, when the data is written to an incorrect location within the memory area, or when the program incorrectly calculates the size or location of the data to be written

CVE-2024-22255 is an information disclosure vulnerability in the UHCI USB controller of VMware ESXi, Workstation, and Fusion. A malicious actor with administrative access to a VM may be able to exploit this issue to leak memory from the VMX process.

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Pieter Arntz

Malware Intelligence Researcher

Was a Microsoft MVP in consumer security for 12 years running. Can speak four languages. Smells of rich mahogany and leather-bound books.