# CVE-2025-71070: ublk: clean up user copy references on ublk server exit

> A reference count leak in the Linux kernel ublk driver allows use-after-free conditions when the ublk server exits, potentially leading to code execution or crashes.

- **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:** 13 Jan 2026
- **Updated:** 5 Aug 2026
- **Also known as:** BELL-CVE-2025-71070, DEBIAN-CVE-2025-71070, GHSA-p797-qv57-j9x8, UBUNTU-CVE-2025-71070

## What is CVE-2025-71070?

CVE-2025-71070 is a high-severity use after free vulnerability in Linux, published on 13 Jan 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:

ublk: clean up user copy references on ublk server exit

If a ublk server process releases a ublk char device file, any requests
dispatched to the ublk server but not yet completed will retain a ref
value of UBLK_REFCOUNT_INIT. Before commit e63d2228ef83 ("ublk: simplify
aborting ublk request"), __ublk_fail_req() would decrement the reference
count before completing the failed request. However, that commit
optimized __ublk_fail_req() to call __ublk_complete_rq() directly
without decrementing the request reference count.
The leaked reference count incorrectly allows user copy and zero copy
operations on the completed ublk request. It also triggers the
WARN_ON_ONCE(refcount_read(&io->ref)) warnings in ublk_queue_reinit()
and ublk_deinit_queue().
Commit c5c5eb24ed61 ("ublk: avoid ublk_io_release() called after ublk
char dev is closed") already fixed the issue for ublk devices using
UBLK_F_SUPPORT_ZERO_COPY or UBLK_F_AUTO_BUF_REG. However, the reference
count leak also affects UBLK_F_USER_COPY, the other reference-counted
data copy mode. Fix the condition in ublk_check_and_reset_active_ref()
to include all reference-counted data copy modes. This ensures that any
ublk requests still owned by the ublk server when it exits have their
reference counts reset to 0.

## Which versions are affected by CVE-2025-71070?


## How do I fix CVE-2025-71070?

Apply the vendor's patch.

## Is CVE-2025-71070 being exploited?

There is no known exploitation of CVE-2025-71070 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-71070 and fix it if it is affected.

What it is: CVE-2025-71070 is a high-severity use after free vulnerability in Linux, published on 13 Jan 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-2025-71070 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-2025-71070/ (Markdown: https://insights.sbomify.com/CVE-2025-71070/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-71070
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-71070
- OSV: https://osv.dev/vulnerability/CVE-2025-71070

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-71070/
Summaries are generated and may contain mistakes; the official description above is the record.