# CVE-2026-55392: NILFS utilities - Undefined Behavior and Out-of-Memory via Unvalidated s_log_block_size

> Attackers can crash NILFS2 utilities by providing crafted filesystem images with invalid block sizes, causing out-of-memory errors or undefined behavior.

- **Severity:** Medium 6.7 (`CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:A/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 18 Jun 2026
- **Updated:** 14 Jul 2026
- **Also known as:** AZL-90200, DEBIAN-CVE-2026-55392, GHSA-f559-vgh2-9hj6, MGASA-2026-0280, OESA-2026-2795, OESA-2026-2796, OESA-2026-2797, OESA-2026-2840, UBUNTU-CVE-2026-55392, openSUSE-SU-2026:11094-1, openSUSE-SU-2026:21183-1

## What is CVE-2026-55392?

CVE-2026-55392 is a medium-severity denial of service vulnerability in nilfs-dev nilfs-utils, published on 18 Jun 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.

### Official description

NILFS utilities through 2.3.0, fixed in commit 26efb5d, nilfs_sb_is_valid() function fails to validate s_log_block_size field in NILFS2 superblock before bit-shift operations. Attackers supplying crafted NILFS2 images trigger undefined behavior through oversized shifts or out-of-memory conditions, crashing tools like nilfs-tune and dumpseg.

Weakness: CWE-1284 (Improper Validation of Specified Quantity in Input)

## Which versions are affected by CVE-2026-55392?


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `nilfs-utils` | openSUSE:Leap 16.0 | All versions | 2.2.9-bp160.2.1 |
| `nilfs-utils` | openSUSE:Tumbleweed | All versions | 2.3.1-1.1 |

## How do I fix CVE-2026-55392?

Apply the vendor's patch.

## Is CVE-2026-55392 being exploited?

There is no known exploitation of CVE-2026-55392 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-55392 and fix it if it is affected.

What it is: CVE-2026-55392 is a medium-severity denial of service vulnerability in nilfs-dev nilfs-utils, published on 18 Jun 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-55392 in the wild and no public exploit code.

Affected product: nilfs-dev nilfs-utils. 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-2026-55392/ (Markdown: https://insights.sbomify.com/CVE-2026-55392/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-55392
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-55392
- OSV: https://osv.dev/vulnerability/CVE-2026-55392

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-55392/
Summaries are generated and may contain mistakes; the official description above is the record.