CVE-2025-40248: Critical vsock Vulnerability in Linux Kernel Resolved

Overview

CVE-2025-40248 identifies a vulnerability within the Linux kernel’s Virtual Socket (vsock) implementation. This flaw stems from improper handling of signals and timeouts during the connect() system call when a socket is already established. Ignoring these signals could lead to various race conditions, use-after-free scenarios, and other unpredictable behaviors, potentially impacting system stability and security.

Technical Details

The core of the vulnerability lies in the kernel’s reaction to signals (like interrupts or timeouts) received during the connect() process for a vsock that is already in an established state. Disconnecting the socket in response to these signals triggers a sequence of events that can introduce several problems:

1. Race Condition with Credit Management: The connect() function could call vsock_transport_cancel_pkt(), which in turn calls virtio_transport_purge_skbs(). This process can race with sendmsg(), which calls virtio_transport_get_credit(). This race can lead to an inaccurate vvs->bytes_unsent value, confusing the SOCK_LINGER handling.
2. Sockmap Corruption: Resetting the state of a connected socket due to a signal can race with the socket being placed within a sockmap. A disconnected socket residing in a sockmap violates the sockmap’s assumptions, triggering warnings and potentially leading to errors.
3. State Transition and Use-After-Free: Transitioning a socket from SS_CONNECTED back to SS_UNCONNECTED after TCP_ESTABLISHED allows for transport changes or drops, which creates a potential use-after-free or null-pointer dereference if sendmsg() or another connect() call occurs simultaneously.

The fix implemented addresses this issue by preventing disconnection of the socket upon receiving a signal or timeout if the socket is already established. The original logic for unconnected sockets (no lingering, no sockmap placement, rejection by sendmsg()) is retained.

CVSS Analysis

As of the publication date (2025-12-04T16:16:18.240), a CVSS score has not been assigned to CVE-2025-40248. The severity is currently listed as N/A. A complete risk assessment requires further analysis and should be conducted by security professionals considering the specific context of affected systems.

Possible Impact

The vulnerability could potentially lead to:

• System Instability: Race conditions and unexpected state transitions could cause kernel panics or other forms of system crashes.
• Denial of Service: Exploiting the vulnerability could potentially lead to a denial-of-service condition.
• Security Risks: Although the provided information doesn’t explicitly mention privilege escalation or information disclosure, the potential for use-after-free vulnerabilities warrants a cautious approach.

Mitigation or Patch Steps

The vulnerability has been addressed in the Linux kernel. Users are strongly advised to update their kernels to a version containing the fix. Check your distribution’s security advisories for specific instructions on how to update. The relevant commits are available in the stable kernel tree.

References

• Kernel Commit 1
• Kernel Commit 2
• Kernel Commit 3
• Kernel Commit 4
• Kernel Commit 5
• Mailing List Discussion 1
• Mailing List Discussion 2
• Mailing List Discussion 3