CVE-2024-26327 - Buffer Overflow Vulnerability in QEMU due to Mishandling of NumVFs and TotalVFs in PCIe SR-IOV

Security researchers have recently discovered a critical vulnerability in QEMU, a popular open-source software that provides hardware emulation and virtualization. QEMU versions 7.1. through 8.2.1 are affected by this issue, which is tracked under the identifier CVE-2024-26327. This vulnerability stems from a buffer overflow caused by improper handling of NumVFs (Number of Virtual Functions) and TotalVFs (Total Virtual Functions) in the PCIe SR-IOV (Single Root I/O Virtualization) implementation.

Detailed Analysis

The vulnerability resides in the "register_vfs()" function in the "hw/pci/pcie_sriov.c" source file. In scenarios where a guest writes a NumVFs value greater than the TotalVFs value, this function mishandles the overflow situation and results in a buffer overflow, leading to potential exploitation by attackers.

Consider the following code snippet from "hw/pci/pcie_sriov.c"

static void register_vfs(PCIDevice *pdev, uint16_t num_vfs)
{
    // ... Snipped for brevity ...
    uint16_t total_vfs = pci_get_word(pdev->wmask + pos + PCI_SRIOV_TOTAL_VF);
    // ... Snipped for brevity ...
    for (i = ; i < num_vfs; i++) {
        vf = pci_sriov_create_vf(pdev, i, &local_err);
        // ... Snipped for brevity ...
    }
}

In the above code snippet, we can see that the loop iterates for "num_vfs" times. However, there is no prior check to ensure that "num_vfs" is not greater than "total_vfs". This oversight can cause a buffer overflow when the code inside the loop attempts to create and register virtual functions beyond the allocated limit.

Original References

- QEMU's Official Repository: https://git.qemu.org/?p=qemu.git;a=commit;h=01d7f87
- QEMU's Official Documentation: https://www.qemu.org/

Exploit Details

An attacker can exploit this vulnerability by crafting a malicious VM that writes a larger "num_vfs" value than the "total_vfs" value, causing a buffer overflow. This could potentially lead to arbitrary code execution, privilege escalation, or even denial of service (DoS), depending on the underlying system architecture and configuration.

Mitigation

Users who are running vulnerable QEMU versions should immediately upgrade to the latest version available. It is also crucial to tailor the configuration of your virtualization environment by closely monitoring and restricting untrusted guests and virtual machines.

Conclusion

CVE-2024-26327 is a critical buffer overflow vulnerability in QEMU affecting versions 7.1. through 8.2.1. The issue lies in improper handling of NumVFs and TotalVFs in the PCIe SR-IOV implementation. To prevent exploitation, users should update their QEMU installations and apply the necessary precautions when managing virtual machines and guests.

Timeline

Published on: 02/19/2024 05:15:22 UTC
Last modified on: 04/19/2024 07:15:09 UTC