CVE-2023-53020 l2tp: close all race conditions in l2tp_tunnel_register()

What is CVE-2023-53020?

CVE-2023-53020 is a medium-severity vulnerability in Linux kernel, published on 27 Mar 2025. It can only be exploited from the same machine or local network, with no action from the victim.

Official description

In the Linux kernel, the following vulnerability has been resolved:

l2tp: close all race conditions in l2tp_tunnel_register()

The code in l2tp_tunnel_register() is racy in several ways:

1. It modifies the tunnel socket _after_ publishing it.

2. It calls setup_udp_tunnel_sock() on an existing socket without locking.

3. It changes sock lock class on fly, which triggers many syzbot reports.

This patch amends all of them by moving socket initialization code before publishing and under sock lock. As suggested by Jakub, the l2tp lockdep class is not necessary as we can just switch to bh_lock_sock_nested().

Weakness: CWE-362

Which versions are affected by CVE-2023-53020?

It affects 1 product.

Products include Linux kernel.

How do I fix CVE-2023-53020?

Apply the vendor's patch.

Is CVE-2023-53020 being exploited?

There is no known exploitation of CVE-2023-53020 in the wild and no public exploit code.

Other vulnerabilities in Linux kernel

• CVE-2026-53266 Linux Kernel Out-of-Bounds Write Exploited High 8.8
• CVE-2013-6282 Linux Kernel Improper Input Validation Exploited High 8.8
• CVE-2022-0185 Linux Kernel Heap-Based Buffer Overflow Exploited High 8.4
• CVE-2013-2094 Linux Kernel Privilege Escalation Exploited High 8.4
• CVE-2026-53362 Linux Kernel Unspecified Exploited High 7.8

All Linux kernel vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as BELL-CVE-2023-53020, DEBIAN-CVE-2023-53020, GHSA-7fmf-h6vh-qp27, UBUNTU-CVE-2023-53020.