# CVE-2026-23319: bpf: Fix a UAF issue in bpf_trampoline_link_cgroup_shim

> A use-after-free in the Linux kernel's BPF subsystem allows attackers to execute arbitrary code or escalate privileges via race conditions.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **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:** Yes
- **Published:** 25 Mar 2026
- **Updated:** 15 Oct 2026
- **Also known as:** AZL-80691, BELL-CVE-2026-23319, DEBIAN-CVE-2026-23319, GHSA-65x4-mv56-gf8m, ROOT-OS-DEBIAN-12-CVE-2026-23319, ROOT-OS-DEBIAN-13-CVE-2026-23319, ROOT-OS-UBUNTU-2404-CVE-2026-23319, UBUNTU-CVE-2026-23319

## What is CVE-2026-23319?

CVE-2026-23319 is a high-severity use after free 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:

bpf: Fix a UAF issue in bpf_trampoline_link_cgroup_shim

The root cause of this bug is that when 'bpf_link_put' reduces the
refcount of 'shim_link->link.link' to zero, the resource is considered
released but may still be referenced via 'tr->progs_hlist' in
'cgroup_shim_find'. The actual cleanup of 'tr->progs_hlist' in
'bpf_shim_tramp_link_release' is deferred. During this window, another
process can cause a use-after-free via 'bpf_trampoline_link_cgroup_shim'.

Based on Martin KaFai Lau's suggestions, I have created a simple patch.

To fix this:
   Add an atomic non-zero check in 'bpf_trampoline_link_cgroup_shim'.
   Only increment the refcount if it is not already zero.

Testing:
   I verified the fix by adding a delay in
   'bpf_shim_tramp_link_release' to make the bug easier to trigger:

static void bpf_shim_tramp_link_release(struct bpf_link *link)
{
	/* ... */
	if (!shim_link->trampoline)
		return;

+	msleep(100);
	WARN_ON_ONCE(bpf_trampoline_unlink_prog(&shim_link->link,
		shim_link->trampoline, NULL));
	bpf_trampoline_put(shim_link->trampoline);
}

Before the patch, running a PoC easily reproduced the crash(almost 100%)
with a call trace similar to KaiyanM's report.
After the patch, the bug no longer occurs even after millions of
iterations.

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2026-23319?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-23319?

Apply the vendor's patch.

## Is CVE-2026-23319 being exploited?

There is no known exploitation of CVE-2026-23319 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-23319 and fix it if it is affected.

What it is: CVE-2026-23319 is a high-severity use after free 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.
Exploitation: There is no known exploitation of CVE-2026-23319 in the wild and no public exploit code.

Affected product: Linux kernel. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-23319/ (Markdown: https://insights.sbomify.com/CVE-2026-23319/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-23319
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-23319
- OSV: https://osv.dev/vulnerability/CVE-2026-23319

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-23319/
Summaries are generated and may contain mistakes; the official description above is the record.