# CVE-2026-53320: nilfs2: reject zero bd_oblocknr in nilfs_ioctl_mark_blocks_dirty()

> A local attacker can trigger a kernel warning and potential denial of service by sending a crafted ioctl request with a zero block number to the nilfs2 filesystem.

- **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:** 26 Jun 2026
- **Updated:** 26 Jun 2026
- **Also known as:** BELL-CVE-2026-53320, DEBIAN-CVE-2026-53320, GHSA-r88h-63mh-cc6h, ROOT-OS-DEBIAN-11-CVE-2026-53320, ROOT-OS-DEBIAN-12-CVE-2026-53320, ROOT-OS-UBUNTU-2204-CVE-2026-53320, ROOT-OS-UBUNTU-2404-CVE-2026-53320, UBUNTU-CVE-2026-53320

## What is CVE-2026-53320?

CVE-2026-53320 is a medium-severity vulnerability in Linux kernel, published on 26 Jun 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:

nilfs2: reject zero bd_oblocknr in nilfs_ioctl_mark_blocks_dirty()

nilfs_ioctl_mark_blocks_dirty() uses bd_oblocknr to detect dead blocks
by comparing it with the current block number bd_blocknr. If they differ,
the block is considered dead and skipped.

However, bd_oblocknr should never be 0 since block 0 typically stores the
primary superblock and is never a valid GC target block. A corrupted ioctl
request with bd_oblocknr set to 0 causes the comparison to incorrectly
match when the lookup returns -ENOENT and sets bd_blocknr to 0, bypassing
the dead block check and calling nilfs_bmap_mark() on a non-existent
block. This causes nilfs_btree_do_lookup() to return -ENOENT, triggering
the WARN_ON(ret == -ENOENT).

Fix this by rejecting ioctl requests with bd_oblocknr set to 0 at the
beginning of each iteration.

[ryusuke: slightly modified the commit message and comments for accuracy]

## Which versions are affected by CVE-2026-53320?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-53320?

Apply the vendor's patch.

## Is CVE-2026-53320 being exploited?

There is no known exploitation of CVE-2026-53320 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-2026-53320 and fix it if it is affected.

What it is: CVE-2026-53320 is a medium-severity vulnerability in Linux kernel, published on 26 Jun 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-2026-53320 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-2026-53320/ (Markdown: https://insights.sbomify.com/CVE-2026-53320/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-53320
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-53320
- OSV: https://osv.dev/vulnerability/CVE-2026-53320

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-53320/
Summaries are generated and may contain mistakes; the official description above is the record.