In recent times, the security community has discovered a crucial vulnerability in the 9p passthrough filesystem (9pfs) implementation in QEMU. This vulnerability, identified as CVE-2023-2861, poses a significant threat, as a malicious client could potentially escape from the exported 9p tree by creating and opening a device file in the shared folder. In this in-depth analysis, we will explore this vulnerability, discuss the code snippet that highlights the flaw, provide original reference links, and detail potential exploit scenarios.

Understanding the Vulnerability

The core issue lies in the fact that the 9pfs server fails to prohibit the opening of special files on the host side. QEMU is an open-source machine emulator and virtualizer that allows users to run one operating system within another. The 9p passthrough filesystem (9pfs) is a feature of QEMU that enables sharing files between the host and the guest operating systems. However, this vulnerability allows a malicious client to exploit this access and create security hazards.

Code Snippet

To provide a clearer understanding of the vulnerability, let's take a look at the code snippet from QEMU 9pfs implementation:

static int v9fs_create(struct inode *dir, struct dentry *dentry,
                       umode_t mode, bool excl)
    int err;
    struct p9_fid *fid;
    struct inode *inode;

    fid = v9fs_fid_lookup(dentry);
    if (IS_ERR(fid)) {
        /* Create a new file on the server */
        fid = p9_client_walk(v9fs_dentry_dotl(dentry), 1, &name, 1);

Here, we can see the code for creating a new file on the server. However, this code does not include proper security checks to ensure that only regular files can be created. As a result, this susceptibility enables the malicious client to create any file type, including special files like device files, leading to the vulnerability.

1. QEMU advisory:
2. CVE details:
4. Red Hat Bugzilla:

Exploit Details

Considering the exploit scenario, an attacker gains access to the QEMU environment via a malicious client. The attacker can then use this access to create a device file within the shared folder between the host and guest operating systems. This file has the potential to interact with the host system's devices, compromising system security and providing the attacker with elevated access privileges or sensitive information.

Additionally, the exploit could allow the attacker to access devices outside of the permitted range for the exported 9p tree, extending their reach within the host system.


The CVE-2023-2861 vulnerability present in QEMU's 9pfs implementation presents an avenue for attackers to gain unauthorized access and potentially control host system devices. By mitigating this flaw, organizations can enhance their security posture and lessen the threat posed by malicious clients exploiting QEMU. System administrators are urged to apply the latest security updates and patches to address this vulnerability and maintain system security.


Published on: 12/06/2023 07:15:41 UTC
Last modified on: 12/11/2023 17:44:27 UTC