A security vulnerability has been identified in the Linux kernel, specifically within the XFRM subsystem. This flaw, designated as CVE-2023-39194, can potentially lead to an information disclosure by an attacker with local privileged access (CAP_NET_ADMIN). In this in-depth article, we will explore the vulnerability details, code snippets, original references, and real-life exploitation scenarios. We will also provide you with mitigation techniques to secure your systems effectively.

Vulnerability Details

CVE-2023-39194 pertains to a flaw found in the XFRM subsystem in the Linux kernel that can result in an out-of-bounds read, which in turn may leak sensitive information. The vulnerability occurs when processing state filters, enabling an attacker to read past the end of an allocated buffer.

For those unfamiliar with XFRM, it is a vital component within the Linux kernel responsible for implementing the IPsec protocol suite, which provides secure networking features such as confidentiality, integrity, and authentication for IP packets.

Code Snippets

The following code snippet demonstrates a portion of the vulnerable code in the Linux kernel XFRM subsystem (file: "xfrm_user.c"):

static int xfrm_state_filter_match(const struct xfrm_state *x,
                                   const struct xfrm_state_filter *filt)
    if (filt->id.daddr.family != AF_UNSPEC) {
        // ... code omitted for brevity ...

    // ... more code ...

    return 1;

The issue lies in the improper validation of the received state filter (filt). In specific input circumstances, the function xfrm_state_filter_match() can read past the end of the memory buffer allocated to the filter, potentially leading to information disclosure.

Exploit Details

An attacker who has local system access and the CAP_NET_ADMIN capability can exploit this vulnerability to trigger an out-of-bounds read, potentially disclosing sensitive information. In practice, this can be achieved through a crafted XFRM-related system call that uses a specifically designed state filter in order to trigger the vulnerability.

While the possibility of remote exploitation seems remote, in specific scenarios where the attacker has control over a virtual machine within a virtualized environment, this could eventually escalate into a more serious, cross-guest scenario.

Linux kernel source code

* <https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git>

XFRM Subsystem documentation

* <https://www.kernel.org/doc/html/latest/networking/xfrm_sysctl.html>

CVE-2023-39194 entry with more details

* <https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2023-39194>

To protect your systems from this vulnerability, we recommend the following steps

1. Keep your kernel updated: Ensure that your Linux kernel is updated to the latest version, which should include patches for this vulnerability. Regularly updating your kernel and system packages can help protect your systems from newly discovered security vulnerabilities.

2. Restrict local system access: Because this exploitation requires local access and the CAP_NET_ADMIN capability, it's essential to limit the number of users with such access on your systems.

3. Monitor system logs: Regularly monitor your systems for any suspicious activity that might indicate an attempted exploitation of this vulnerability.


CVE-2023-39194 is a critical vulnerability affecting the Linux kernel's XFRM subsystem. By understanding the underlying concepts, code snippets, and exploitation techniques, security professionals and system administrators can better protect their environments from this type of attack. Always ensure that your systems are updated and follow best security practices to minimize the risk of security vulnerabilities.


Published on: 10/09/2023 18:15:10 UTC
Last modified on: 11/07/2023 04:17:28 UTC