# CVE-2025-70100: lwext4 divide-by-zero in ext4_block_set_lb_size

Source: https://junglewise.ai/threats/cve-2025-70100-lwext4-divide-by-zero-in-ext4-block-set-lb-size  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-06-03. Updated: 2026-06-03  
License: CC BY 4.0 with a link back

CVE-2025-70100 · Severity: info · CVSS 5.5 · Published 2026-06-03

A vulnerability in the lwext4 library, which is used to provide ext4 filesystem support for microcontrollers and embedded systems, could allow an attacker to crash an application. By providing a specially crafted, malicious filesystem image, an attacker can trigger a system crash when the software attempts to mount or process the image. This results in a denial of service, potentially impacting the availability of embedded devices or systems relying on this library for data storage.

Technologies: [Grzegorz Kostka Lwext4](https://junglewise.ai/threats/technologies/lwext4). Vendors: [Grzegorz Kostka](https://junglewise.ai/threats/vendors/grzegorz-kostka).

## Quick answers

**Is CVE-2025-70100 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2025-70100 being exploited in the wild.

**How severe is CVE-2025-70100?** Informational severity, with a CVSS score of 5.5, published 3 June 2026.

**Which products and versions are affected?** Grzegorz Kostka Lwext4 1.0.0.

**Is there a fix for CVE-2025-70100?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2025-70100 attacked?** It is attacked with local access, in a software library.

**Am I affected by CVE-2025-70100?** Check whether you run Grzegorz Kostka Lwext4 at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

A divide-by-zero vulnerability exists in the ext4_block_set_lb_size function within src/ext4_blockdev.c of the lwext4 1.0.0 library. The root cause is a lack of validation for the logical block size (lb_size) parameter; when a crafted ext4 image with a zero logical block size is processed during an ext4_mount operation, the library performs arithmetic division by zero. This leads to a Floating-Point Exception (FPE) and a subsequent runtime crash. The attack requires the victim to attempt to mount or process a malicious filesystem image. As of the advisory date, the issue was reported via GitHub issues and demonstrated with a proof-of-concept (PoC) using AFL fuzzing.

## Affected products

- gkostka lwext4 1.0.0

## Timeline

- 2025-12-09: disclosed: Issue reported on GitHub repository
- 2026-06-03: advisory: CVE-2025-70100 published in NVD

## References

- [https://github.com/gkostka/lwext4/issues/90](https://github.com/gkostka/lwext4/issues/90)
- [https://github.com/sigdevel/pocs/blob/main/res/lwext4/2/sig8_2_lwext4_ext4_blockdev_c_127](https://github.com/sigdevel/pocs/blob/main/res/lwext4/2/sig8_2_lwext4_ext4_blockdev_c_127)
- [https://infosec.exchange/@sigdevel/116668952003072580](https://infosec.exchange/@sigdevel/116668952003072580)

## Related threats

- [gkostka lwext4 out-of-bounds read in ext4_ext_binsearch_idx](https://junglewise.ai/threats/cve-2025-70101-gkostka-lwext4-out-of-bounds-read-in-ext4-ext-binsearch-idx)
- [lwext4 NULL pointer dereference in ext4_dir_en_get_name_len](https://junglewise.ai/threats/cve-2025-70099-lwext4-null-pointer-dereference-in-ext4-dir-en-get-name-len)