# CVE-2025-70101: gkostka lwext4 out-of-bounds read in ext4_ext_binsearch_idx

Source: https://junglewise.ai/threats/cve-2025-70101-gkostka-lwext4-out-of-bounds-read-in-ext4-ext-binsearch-idx  
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-2025-70101 · Severity: info · CVSS 5.5 · Published 2026-06-03

A vulnerability in the lwext4 library, which provides ext4 filesystem support for embedded systems, could allow an attacker to crash applications using the library. By providing a specially crafted or corrupted filesystem image, an attacker can trigger a memory error that leads to a denial of service. This could impact the availability of devices or software that automatically mount or read external storage media.

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

## Quick answers

**Is CVE-2025-70101 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2025-70101 being exploited in the wild.

**How severe is CVE-2025-70101?** 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-2025-70101?** 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-2025-70101 attacked?** It is attacked with local access, in a software library.

**Am I affected by CVE-2025-70101?** 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

An out-of-bounds read exists in the ext4_ext_binsearch_idx function within src/ext4_extent.c of lwext4 1.0.0. The vulnerability is caused by insufficient validation of the extent header fields (specifically eh_entries and eh_depth) before performing a binary search over extent index entries. If a crafted filesystem image contains an internal node where eh_depth is greater than zero but eh_entries is zero, the EXT_FIRST_INDEX and EXT_LAST_INDEX macros return invalid pointers. This leads to invalid pointer calculations and a subsequent out-of-bounds memory read (segmentation fault) during extent tree traversal. Attackers can exploit this by providing a malicious filesystem image to be processed by the library.

## Affected products

- gkostka lwext4 1.0.0

## Timeline

- 2025-12-09: disclosed: Issue reported on GitHub
- 2026-06-03: advisory: NVD published CVE-2025-70101

## References

- [https://github.com/gkostka/lwext4/issues/91](https://github.com/gkostka/lwext4/issues/91)
- [https://github.com/sigdevel/pocs/blob/main/res/lwext4/3/sig11_lwext4_ext4_extent_815](https://github.com/sigdevel/pocs/blob/main/res/lwext4/3/sig11_lwext4_ext4_extent_815)
- [https://infosec.exchange/@sigdevel/116668958927817708](https://infosec.exchange/@sigdevel/116668958927817708)

## Related threats

- [lwext4 divide-by-zero in ext4_block_set_lb_size](https://junglewise.ai/threats/cve-2025-70100-lwext4-divide-by-zero-in-ext4-block-set-lb-size)
- [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)