# CVE-2026-64535: nvmet-tcp: Fix potential UAF when ddgst mismatch

> A use-after-free vulnerability in the Linux kernel's NVMe/TCP driver allows attackers to cause denial of service or potentially execute code when data digest mismatches occur.

- **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-2026-64535, DEBIAN-CVE-2026-64535, GHSA-5wfv-mpg7-6vcr, ROOT-OS-DEBIAN-12-CVE-2026-64535, UBUNTU-CVE-2026-64535

## What is CVE-2026-64535?

CVE-2026-64535 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: Fix potential UAF when ddgst mismatch

Shivam Kumar found via vulnerability testing:
When data digest is enabled on an NVMe/TCP connection and a digest
mismatch occurs on a non-final H2C_DATA PDU during an R2T-based
data transfer, the digest error handler in nvmet_tcp_try_recv_ddgst()
calls nvmet_req_uninit() — which performs percpu_ref_put() on the
submission queue — but does NOT mark the command as completed. It
does not set cqe->status, does not modify rbytes_done, and does not
clear any flag. When the subsequent fatal error triggers queue
teardown, nvmet_tcp_uninit_data_in_cmds() iterates all commands,
checks nvmet_tcp_need_data_in() for each one, and finds that the
already-uninited command still appears to need data (because
rbytes_done < transfer_len and cqe->status == 0). It therefore calls
nvmet_req_uninit() a second time on the same command — a double
percpu_ref_put against a single percpu_ref_get.

Weakness: CWE-415 (Double Free)

## Which versions are affected by CVE-2026-64535?


## How do I fix CVE-2026-64535?

Apply the vendor's patch.

## Is CVE-2026-64535 being exploited?

There is no known exploitation of CVE-2026-64535 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-64535 and fix it if it is affected.

What it is: CVE-2026-64535 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-2026-64535 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-2026-64535/ (Markdown: https://insights.sbomify.com/CVE-2026-64535/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-64535
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-64535
- OSV: https://osv.dev/vulnerability/CVE-2026-64535

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-64535/
Summaries are generated and may contain mistakes; the official description above is the record.