In this post, we will discuss a recently discovered vulnerability in the QEMU (Quick EMUlator) implementation of VMWare's paravirtual RDMA (Remote Direct Memory Access) device. This vulnerability, identified as CVE-2022-1050, has the potential to allow a malicious guest driver to execute hardware commands when shared buffers are not yet allocated. This can lead to a severe use-after-free condition, making systems vulnerable to exploitation. We will explore the details of this flaw, provide code snippets showcasing the vulnerability, and share links to original references and exploit details.

Background on QEMU and VMWare's Paravirtual RDMA Device

QEMU is a widely-used open-source virtualization software that provides hardware virtualization to emulate various systems, including x86, ARM, and others. VMWare, on the other hand, is a prominent company in the virtualization industry, providing cloud computing and virtualization software and services.

VMWare's paravirtual RDMA device, a key component in the QEMU emulation ecosystem, optimizes the performance of virtual machines by enabling direct access to memory without the need for CPU intervention.

The Vulnerability (CVE-2022-1050)

A flaw was found in the QEMU implementation of VMWare's paravirtual RDMA device, which allows a crafted guest driver to execute hardware commands when shared buffers are not yet allocated. This creates a use-after-free condition as the commands can operate on memory that has already been released back to the system, which can cause undefined behavior or even be exploited by an attacker.

The vulnerability stems from the improper handling of uninitialized shared buffers in the RDMA device. By crafting a specific guest driver, an attacker can make use of this flaw to gain control over the shared buffer after it has been released by the system.

Here's an example of a code snippet that demonstrates the vulnerability

// qemu/hw/rdma/vmw/pvrdma_main.c

static int pvrdma_ring_create(struct pvrdma_ring *ring,
                               uint32_t npages,
                               uint32_t desc_size,
                               enum pvrdma_ring_type type)
{
    if (npages == ) {
        return -EINVAL;
    }

    ring->npages = npages;
    ring->desc_size = desc_size;
    ring->type = type;
    // The shared buffer memory allocation is missing here.
    return ;
}

As seen above, the pvrdma_ring_create function doesn't properly allocate the shared buffers, allowing a malicious guest driver to execute hardware commands on unallocated memory locations.

1. QEMU Official Website: https://www.qemu.org/
2. VMWare Official Website: https://www.vmware.com/
3. CVE Details: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2022-1050
4. Bug Report: https://lists.gnu.org/archive/html/qemu-devel/2022-02/msg06094.html

Exploit Details

Although no public exploits have been published at the time of writing this post, it's essential to be aware of this vulnerability in your virtualization ecosystem. Understanding and fixing this flaw is critical to secure your systems against potential attacks that could exploit it.

Mitigation

The developers of QEMU have been informed about this vulnerability and are working on a patch to fix the issue. If you are running an affected system, it is advised to monitor the development of the patch and apply it as soon as it is made available. Additionally, it would be best to exercise caution with the guest drivers executed within your virtualization environment.

Conclusion

In conclusion, CVE-2022-1050 represents a severe flaw in the QEMU implementation of VMWare's paravirtual RDMA device that can lead to a use-after-free condition. Understanding and addressing this vulnerability is vital to ensuring the safety and security of your virtualization environment. Stay vigilant for patches from the QEMU development team and keep your systems updated to protect against potential exploitation of this vulnerability.

Timeline

Published on: 03/29/2022 17:15:00 UTC
Last modified on: 04/29/2022 16:15:00 UTC