# CVE-2025-68366: nbd: defer config unlock in nbd_genl_connect

> A use-after-free in the Linux kernel NBD driver allows local attackers to cause a crash or potentially escalate privileges via race conditions.

- **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:** 24 Dec 2025
- **Updated:** 16 Jun 2026
- **Also known as:** AZL-73081, BELL-CVE-2025-68366, DEBIAN-CVE-2025-68366, GHSA-9x47-h3pc-w4pg, ROOT-OS-DEBIAN-11-CVE-2025-68366, ROOT-OS-DEBIAN-12-CVE-2025-68366, ROOT-OS-UBUNTU-2204-CVE-2025-68366, ROOT-OS-UBUNTU-2404-CVE-2025-68366, UBUNTU-CVE-2025-68366

## What is CVE-2025-68366?

CVE-2025-68366 is an use after free vulnerability in Linux, published on 24 Dec 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:

nbd: defer config unlock in nbd_genl_connect

There is one use-after-free warning when running NBD_CMD_CONNECT and
NBD_CLEAR_SOCK:

nbd_genl_connect
  nbd_alloc_and_init_config // config_refs=1
  nbd_start_device // config_refs=2
  set NBD_RT_HAS_CONFIG_REF			open nbd // config_refs=3
  recv_work done // config_refs=2
						NBD_CLEAR_SOCK // config_refs=1
						close nbd // config_refs=0
  refcount_inc -> uaf

------------[ cut here ]------------
refcount_t: addition on 0; use-after-free.
WARNING: CPU: 24 PID: 1014 at lib/refcount.c:25 refcount_warn_saturate+0x12e/0x290
 nbd_genl_connect+0x16d0/0x1ab0
 genl_family_rcv_msg_doit+0x1f3/0x310
 genl_rcv_msg+0x44a/0x790

The issue can be easily reproduced by adding a small delay before
refcount_inc(&nbd->config_refs) in nbd_genl_connect():

        mutex_unlock(&nbd->config_lock);
        if (!ret) {
                set_bit(NBD_RT_HAS_CONFIG_REF, &config->runtime_flags);
+               printk("before sleep\n");
+               mdelay(5 * 1000);
+               printk("after sleep\n");
                refcount_inc(&nbd->config_refs);
                nbd_connect_reply(info, nbd->index);
        }

## Which versions are affected by CVE-2025-68366?


## How do I fix CVE-2025-68366?

Apply the vendor's patch.

## Is CVE-2025-68366 being exploited?

There is no known exploitation of CVE-2025-68366 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-68366 and fix it if it is affected.

What it is: CVE-2025-68366 is an use after free vulnerability in Linux, published on 24 Dec 2025. 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-2025-68366 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-2025-68366/ (Markdown: https://insights.sbomify.com/CVE-2025-68366/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-68366
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-68366
- OSV: https://osv.dev/vulnerability/CVE-2025-68366

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-68366/
Summaries are generated and may contain mistakes; the official description above is the record.