# CVE-2026-64534: nvmet-tcp: check INIT_FAILED before nvmet_req_uninit in digest error path

> A refcount underflow in the Linux kernel's nvmet-tcp module causes a use-after-free diagnostic and permanent workqueue deadlock, leading to denial of service.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 27 Jul 2026
- **Updated:** 19 Oct 2026
- **Also known as:** BELL-CVE-2026-64534, DEBIAN-CVE-2026-64534, GHSA-6vg3-7hp6-mqc5, ROOT-OS-DEBIAN-12-CVE-2026-64534, UBUNTU-CVE-2026-64534

## What is CVE-2026-64534?

CVE-2026-64534 is a critical use after free vulnerability in Linux, published on 27 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

nvmet-tcp: check INIT_FAILED before nvmet_req_uninit in digest error path

In nvmet_tcp_try_recv_ddgst(), when a data digest mismatch is detected,
nvmet_req_uninit() is called unconditionally. However, if the command
arrived via the nvmet_tcp_handle_req_failure() path, nvmet_req_init()
had returned false and percpu_ref_tryget_live() was never executed. The
unconditional percpu_ref_put() inside nvmet_req_uninit() then causes a
refcount underflow, leading to a WARNING in
percpu_ref_switch_to_atomic_rcu, a use-after-free diagnostic, and
eventually a permanent workqueue deadlock.

Check cmd->flags & NVMET_TCP_F_INIT_FAILED before calling
nvmet_req_uninit(), matching the existing pattern in
nvmet_tcp_execute_request().

Weakness: CWE-667 (Improper Locking)

## Which versions are affected by CVE-2026-64534?


## How do I fix CVE-2026-64534?

Apply the vendor's patch.

## Is CVE-2026-64534 being exploited?

There is no known exploitation of CVE-2026-64534 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-64534 and fix it if it is affected.

What it is: CVE-2026-64534 is a critical use after free vulnerability in Linux, published on 27 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-64534 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-2026-64534/ (Markdown: https://insights.sbomify.com/CVE-2026-64534/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-64534
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-64534
- OSV: https://osv.dev/vulnerability/CVE-2026-64534

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-64534/
Summaries are generated and may contain mistakes; the official description above is the record.