# CVE-2026-7007: Division by zero in Zephyr ext2 superblock parsing allows DoS via crafted filesystem image

> Attackers can cause denial of service on Zephyr devices by mounting a crafted ext2 filesystem image with zero block or inode group counts.

- **Severity:** Medium 4.6 (`CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 24 Jul 2026
- **Updated:** 31 Aug 2026
- **Also known as:** GHSA-wrf2-79mm-cvw5

## What is CVE-2026-7007?

CVE-2026-7007 is a medium-severity denial of service vulnerability in Zephyrproject Zephyr, published on 24 Jul 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

The Zephyr ext2 file system validates the on-disk superblock in ext2_verify_disk_superblock() (subsys/fs/ext2/ext2_impl.c) before completing a mount. The validator checked the magic number, block size, revision and feature flags, but did not verify that the on-disk fields s_blocks_per_group and s_inodes_per_group are non-zero. Both fields are read directly from the image and are later used as divisors during mount-time initialization.

During mount, get_ngroups() divides and modulos s_blocks_count by s_blocks_per_group (reached via ext2_fetch_block_group() from ext2_init_fs()), and get_itable_entry() divides (ino - 1) by s_inodes_per_group when fetching the root inode (both in subsys/fs/ext2/ext2_diskops.c). A superblock with either field set to zero therefore causes an integer division by zero during the mount sequence.

An attacker who can present a crafted ext2 image to a device that mounts ext2 — removable media such as an SD card or a USB mass-storage device — can trigger this. On ARMv7-M / ARMv8-M-mainline Cortex-M targets, divide-by-zero trapping is enabled (SCB_CCR_DIV_0_TRP), so the division raises a UsageFault that Zephyr treats as a fatal error, producing a denial of service. The impact is limited to availability; the malformed value is consumed only as a divisor.

The fix rejects a zero s_blocks_per_group or s_inodes_per_group in the superblock validator, returning -EINVAL so the mount fails before any block-group or inode I/O occurs.

Weakness: CWE-369 (Divide By Zero)

## Which versions are affected by CVE-2026-7007?

It affects 1 product.


Products: Zephyrproject Zephyr.

## How do I fix CVE-2026-7007?

No fix has been published for CVE-2026-7007 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-7007 being exploited?

There is no known exploitation of CVE-2026-7007 in the wild and no public exploit code.

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## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-7007 and fix it if it is affected.

What it is: CVE-2026-7007 is a medium-severity denial of service vulnerability in Zephyrproject Zephyr, published on 24 Jul 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-2026-7007 in the wild and no public exploit code.

Affected product: Zephyrproject Zephyr. 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-2026-7007/ (Markdown: https://insights.sbomify.com/CVE-2026-7007/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-7007
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-7007
- OSV: https://osv.dev/vulnerability/CVE-2026-7007

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-7007/
Summaries are generated and may contain mistakes; the official description above is the record.