# CVE-2026-23238: romfs: check sb_set_blocksize() return value

> A local attacker can cause a kernel crash by mounting a romfs filesystem on a loop device with an incompatible block size, leading to denial of service.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/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:** 4 Mar 2026
- **Updated:** 2 Jun 2026
- **Also known as:** BELL-CVE-2026-23238, DEBIAN-CVE-2026-23238, GHSA-wj4m-w3qm-xpch, ROOT-OS-DEBIAN-11-CVE-2026-23238, ROOT-OS-DEBIAN-12-CVE-2026-23238, ROOT-OS-DEBIAN-13-CVE-2026-23238, ROOT-OS-UBUNTU-2204-CVE-2026-23238, ROOT-OS-UBUNTU-2404-CVE-2026-23238, UBUNTU-CVE-2026-23238

## What is CVE-2026-23238?

CVE-2026-23238 is a medium-severity vulnerability in Linux kernel, published on 4 Mar 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:

romfs: check sb_set_blocksize() return value

romfs_fill_super() ignores the return value of sb_set_blocksize(), which
can fail if the requested block size is incompatible with the block
device's configuration.

This can be triggered by setting a loop device's block size larger than
PAGE_SIZE using ioctl(LOOP_SET_BLOCK_SIZE, 32768), then mounting a romfs
filesystem on that device.

When sb_set_blocksize(sb, ROMBSIZE) is called with ROMBSIZE=4096 but the
device has logical_block_size=32768, bdev_validate_blocksize() fails
because the requested size is smaller than the device's logical block
size. sb_set_blocksize() returns 0 (failure), but romfs ignores this and
continues mounting.

The superblock's block size remains at the device's logical block size
(32768). Later, when sb_bread() attempts I/O with this oversized block
size, it triggers a kernel BUG in folio_set_bh():

    kernel BUG at fs/buffer.c:1582!
    BUG_ON(size > PAGE_SIZE);

Fix by checking the return value of sb_set_blocksize() and failing the
mount with -EINVAL if it returns 0.

Weakness: CWE-617 (Reachable Assertion)

## Which versions are affected by CVE-2026-23238?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-23238?

Apply the vendor's patch.

## Is CVE-2026-23238 being exploited?

There is no known exploitation of CVE-2026-23238 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-2026-23238 and fix it if it is affected.

What it is: CVE-2026-23238 is a medium-severity vulnerability in Linux kernel, published on 4 Mar 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-2026-23238 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-2026-23238/ (Markdown: https://insights.sbomify.com/CVE-2026-23238/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-23238
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-23238
- OSV: https://osv.dev/vulnerability/CVE-2026-23238

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-23238/
Summaries are generated and may contain mistakes; the official description above is the record.