# CVE-2024-27036: cifs: Fix writeback data corruption

> A logic error in Linux kernel CIFS writeback causes data corruption when copying files to shares with specific wsize settings.

- **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:** 1 May 2024
- **Updated:** 11 May 2026
- **Also known as:** BELL-CVE-2024-27036, DEBIAN-CVE-2024-27036, GHSA-vc8w-q4f6-f3fg, UBUNTU-CVE-2024-27036

## What is CVE-2024-27036?

CVE-2024-27036 is a high-severity vulnerability in Linux kernel, published on 1 May 2024. 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:

cifs: Fix writeback data corruption

cifs writeback doesn't correctly handle the case where
cifs_extend_writeback() hits a point where it is considering an additional
folio, but this would overrun the wsize - at which point it drops out of
the xarray scanning loop and calls xas_pause().  The problem is that
xas_pause() advances the loop counter - thereby skipping that page.

What needs to happen is for xas_reset() to be called any time we decide we
don't want to process the page we're looking at, but rather send the
request we are building and start a new one.

Fix this by copying and adapting the netfslib writepages code as a
temporary measure, with cifs writeback intending to be offloaded to
netfslib in the near future.

This also fixes the issue with the use of filemap_get_folios_tag() causing
retry of a bunch of pages which the extender already dealt with.

This can be tested by creating, say, a 64K file somewhere not on cifs
(otherwise copy-offload may get underfoot), mounting a cifs share with a
wsize of 64000, copying the file to it and then comparing the original file
and the copy:

        dd if=/dev/urandom of=/tmp/64K bs=64k count=1
        mount //192.168.6.1/test /mnt -o user=...,pass=...,wsize=64000
        cp /tmp/64K /mnt/64K
        cmp /tmp/64K /mnt/64K

Without the fix, the cmp fails at position 64000 (or shortly thereafter).

Weakness: CWE-787 (Out-of-bounds Write)

## Which versions are affected by CVE-2024-27036?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2024-27036?

Apply the vendor's patch.

## Is CVE-2024-27036 being exploited?

There is no known exploitation of CVE-2024-27036 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2024-27036 and fix it if it is affected.

What it is: CVE-2024-27036 is a high-severity vulnerability in Linux kernel, published on 1 May 2024. 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-2024-27036 in the wild and no public exploit code.

Affected product: Linux kernel. 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-2024-27036/ (Markdown: https://insights.sbomify.com/CVE-2024-27036/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2024-27036
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2024-27036
- OSV: https://osv.dev/vulnerability/CVE-2024-27036

---
From sbomify Insights: https://insights.sbomify.com/CVE-2024-27036/
Summaries are generated and may contain mistakes; the official description above is the record.