CVE-2026-23380 tracing: Fix WARN_ON in tracing_buffers_mmap_close

Medium 5.5 Published 25 Mar 2026 Updated 11 May 2026

A local attacker can trigger a kernel warning and potential instability by using madvise to bypass VM_DONTCOPY during fork in the tracing subsystem.

Exploited in the wild: Not known
Login needed: Any signed-in user
Attackable: Local or same network only
Victim action needed: Not needed
Fix: Available

What is CVE-2026-23380?

CVE-2026-23380 is a medium-severity denial of service vulnerability in Linux kernel, published on 25 Mar 2026. 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:

tracing: Fix WARN_ON in tracing_buffers_mmap_close

When a process forks, the child process copies the parent's VMAs but the user_mapped reference count is not incremented. As a result, when both the parent and child processes exit, tracing_buffers_mmap_close() is called twice. On the second call, user_mapped is already 0, causing the function to return -ENODEV and triggering a WARN_ON.

Normally, this isn't an issue as the memory is mapped with VM_DONTCOPY set. But this is only a hint, and the application can call madvise(MADVISE_DOFORK) which resets the VM_DONTCOPY flag. When the application does that, it can trigger this issue on fork.

Fix it by incrementing the user_mapped reference count without re-mapping the pages in the VMA's open callback.

Weakness: CWE-617

Which versions are affected by CVE-2026-23380?

It affects 1 product.

Products include Linux kernel.

How do I fix CVE-2026-23380?

Apply the vendor's patch.

Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.

Is CVE-2026-23380 being exploited?

There is no known exploitation of CVE-2026-23380 in the wild and no public exploit code.

All Linux kernel vulnerabilities

Sources

Also known as BELL-CVE-2026-23380, DEBIAN-CVE-2026-23380, GHSA-q6xr-q445-2xxh, ROOT-OS-DEBIAN-13-CVE-2026-23380, UBUNTU-CVE-2026-23380.