# CVE-2026-90393: bpf: Fix potential UAF in bpf_netns_link_update_prog

> A race condition in the Linux kernel's BPF netns link update allows local attackers to trigger a use-after-free, potentially leading to privilege escalation or code execution.

- **Severity:** Not scored
- **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:** 17 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-101897, BELL-CVE-2026-90393, DEBIAN-CVE-2026-90393, GHSA-9prj-6xm5-hxjf, UBUNTU-CVE-2026-90393

## What is CVE-2026-90393?

CVE-2026-90393 is an use after free vulnerability in Linux, published on 17 Sep 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 potential UAF in bpf_netns_link_update_prog

In bpf_netns_link_update_prog, the checks for old_prog and prog type
are currently performed locklessly before acquiring netns_bpf_mutex.
This creates a race condition that can lead to a UAF issue.

If two threads concurrently execute BPF_LINK_UPDATE on the same netns
link, the following execution path can trigger a UAF:

CPU0                                          CPU1
bpf_netns_link_update_prog
  if (old_prog && old_prog != link->prog)
    return -EPERM;
                                              bpf_netns_link_update_prog
                                                if (old_prog && old_prog != link->prog)
                                                ...
                                                old_prog = xchg(&link->prog, new_prog);
                                                bpf_prog_put(old_prog);
  if (new_prog->type != link->prog->type) <-- trigger UAF

Fix this by moving the old_prog and prog->type checks inside the
netns_bpf_mutex critical section. Meanwhile, use guard() to simplify
lock management and avoid all the goto jumping.

## Which versions are affected by CVE-2026-90393?


## How do I fix CVE-2026-90393?

Apply the vendor's patch.

## Is CVE-2026-90393 being exploited?

There is no known exploitation of CVE-2026-90393 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-90393 and fix it if it is affected.

What it is: CVE-2026-90393 is an use after free vulnerability in Linux, published on 17 Sep 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-2026-90393 in the wild and no public exploit code.

Affected product: Linux. 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-2026-90393/ (Markdown: https://insights.sbomify.com/CVE-2026-90393/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-90393
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-90393
- OSV: https://osv.dev/vulnerability/CVE-2026-90393

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-90393/
Summaries are generated and may contain mistakes; the official description above is the record.