PatchSiren

PatchSiren cyber security CVE debrief

CVE-2026-45918 Linux CVE debrief

A race condition in the Linux kernel's OpenVPN (ovpn) TCP socket handling can cause a NULL pointer dereference crash. When a peer is removed due to keepalive expiration, it enters a release list for socket cleanup. If userspace closes the TCP socket while the peer is in this list, tcp_close() sets sk->sk_socket to NULL. When the release routine later calls ovpn_tcp_socket_detach(), it dereferences this NULL pointer, causing a kernel crash. The fix adds atomic test-and-access of sk->sk_socket under sk->sk_callback_lock to prevent the race.

Vendor
Linux
Product
Unknown
CVSS
MEDIUM 5.5
CISA KEV
Not listed in stored evidence
Original CVE published
2026-05-27
Original CVE updated
2026-06-24
Advisory published
2026-05-27
Advisory updated
2026-06-24

Who should care

Organizations running Linux kernels with the ovpn (kernel-mode OpenVPN) module enabled, particularly those using TCP-based OpenVPN connections. Cloud providers and hosting platforms offering OpenVPN services with kernel acceleration. Embedded systems and network appliances using kernel-mode OpenVPN.

Technical summary

The vulnerability exists in the kernel's ovpn (OpenVPN) driver when handling TCP socket teardown. The race occurs between ovpn_peer_keepalive_work() moving a peer to a release list and concurrent tcp_close() from userspace. The sock_orphan() call in tcp_close() sets sk->sk_socket to NULL, which ovpn_tcp_socket_detach() later dereferences without checking. The fix implements atomic test-and-access under sk->sk_callback_lock to safely handle the potentially NULL sk_socket member.

Defensive priority

high

Recommended defensive actions

  • Apply kernel patches from stable kernel.org commits when available for your distribution
  • Monitor distribution security advisories for updated kernel packages containing the ovpn TCP fix
  • If running OpenVPN in kernel mode (ovpn) with TCP transport, consider temporarily using UDP transport if feasible to avoid the vulnerable code path
  • Review kernel logs for ovpn-related crashes that may indicate exploitation attempts
  • Ensure timely kernel updates on systems using kernel-mode OpenVPN (ovpn) with TCP connections

Evidence notes

CVE description confirms kernel crash via NULL pointer dereference in ovpn TCP socket detach path. Three kernel.org stable commits provided as references. No CVSS score or severity assigned by NVD at time of disclosure.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-45918 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-45918

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2026-45918 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-45918

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

  • Source reference

    Unverified legacy reference

    URL: https://git.kernel.org/stable/c/94560267d6c41b1ff3fafbab726e3f8a55a6af34

    416baaa9-dc9f-4396-8d5f-8c081fb06d67

  • Source reference

    Unverified legacy reference

    URL: https://git.kernel.org/stable/c/b9142cf4e066c825ec68752a7dcaceda700bbe26

    416baaa9-dc9f-4396-8d5f-8c081fb06d67

  • Source reference

    Unverified legacy reference

    URL: https://git.kernel.org/stable/c/f998b2c4bec487063a586695159f9a1856e81c56

    416baaa9-dc9f-4396-8d5f-8c081fb06d67

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.