In the Linux kernel, a critical vulnerability, identified as CVE-2025-21669, has been resolved. The vulnerability specifically targets vsock/virtio and could impact Linux-based systems. This vulnerability is related to the potential null pointer dereference issue that may occur under certain scenarios.
This long-read article aims to provide details about the vulnerability, its resolution through discarding packets when the transport changes in the kernel, and the impact and mitigation measures for the affected Linux-based systems. We will also provide code snippets and links to original references to offer a comprehensive understanding of the subject.
Vulnerability Details
In the Linux kernel, the vsock/virtio vulnerability emerges when an attempt is made to de-assign or assign a socket to a different transport. In these cases, any packets received must be discarded since they are not expected and could lead to issues when accessing vsk->transport.
As described by Hyunwoo Kim in the attached link, a potential scenario occurs when a first connect() is interrupted by a signal, and a second connect() fails. Consequently, vsk->transport can be found at NULL, leading to a NULL pointer dereference. This poses significant risks to Linux-based systems and requires an immediate fix.
Resolution - Discarding Packets If Transport Changes
To resolve the issue, the Linux kernel developers modified the vsock/virtio code to discard packets in cases where the socket has been de-assigned or assigned to another transport.
Here's the code snippet showcasing the resolution
if (vsk->transport != NULL &&
atomic_read(&vsk->peer_shutdown) == ) {
vsock->deliver(vsock, sk);
} else {
vsock->discard(vsock, skb, vsk);
}
The modified code ensures that if the vsk->transport is not NULL and the peer_shutdown value is , the packet is delivered to the transport. Otherwise, the packet is discarded, preventing the NULL pointer dereference issue.
Original References
Details about this vulnerability and its fix can be found in Hyunwoo Kim's original email describing the issue and the patch submitted to the Linux kernel mailing list: Hyunwoo Kim's Email
For further understanding and insights into the Linux kernel and vsock/virtio, you can refer to the following resources:
- Linux Kernel Documentation: Virtio Overview
- Linux Kernel Mailing List: Patch Submission
Exploit Details and Mitigation
As of now, there are no known exploits targeting this specific vulnerability. However, the potential impact of CVE-2025-21669 can be significant, as it leaves Linux-based systems vulnerable to unexpected packet handling, leading to NULL pointer dereference issues.
To mitigate the impact of this vulnerability, users and administrators of Linux-based systems are advised to update their kernel to the latest version containing the fix. Moreover, keeping the system up-to-date with the most recent security patches and following the best practices in system maintenance can help protect against other potential vulnerabilities.
In conclusion, the Linux kernel CVE-2025-21669 is a critical vulnerability that has been addressed by discarding packets if the transport changes, ensuring protection against null pointer dereference issues. By applying the fix and staying vigilant with system updates, Linux users can continue to rely on the stability and security of their systems.
Timeline
Published on: 01/31/2025 12:15:28 UTC
Last modified on: 02/04/2025 15:38:39 UTC