CVE-2026-43438 sched_ext: Remove redundant css_put() in scx_cgroup_init()
A refcount underflow in the Linux kernel scheduler extension allows attackers to trigger a use-after-free, potentially leading to code execution or privilege escalation.
- 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-2026-43438?
CVE-2026-43438 is a high-severity use after free vulnerability in Linux kernel, published on 8 May 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:
sched_ext: Remove redundant css_put() in scx_cgroup_init()
The iterator css_for_each_descendant_pre() walks the cgroup hierarchy under cgroup_lock(). It does not increment the reference counts on yielded css structs.
According to the cgroup documentation, css_put() should only be used to release a reference obtained via css_get() or css_tryget_online(). Since the iterator does not use either of these to acquire a reference, calling css_put() in the error path of scx_cgroup_init() causes a refcount underflow.
Remove the unbalanced css_put() to prevent a potential Use-After-Free (UAF) vulnerability.
Weakness: CWE-416
Which versions are affected by CVE-2026-43438?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-43438?
Apply the vendor's patch.
Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.
Is CVE-2026-43438 being exploited?
There is no known exploitation of CVE-2026-43438 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2026-43438, DEBIAN-CVE-2026-43438, GHSA-h262-73j6-24h2, UBUNTU-CVE-2026-43438.