CVE-2025-70100: A divide-by-zero vulnerability in the ext4_block_set_lb_size function in src/ext4_blockdev.c of the lwext4 1.0

Routine

MEDIUM 5.5DOWNGRADE

CVE-2025-70100 is a medium-severity flaw (CVSS 5.5) affecting lwext4. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

A divide-by-zero vulnerability in the ext4_block_set_lb_size function in src/ext4_blockdev.c of the lwext4 1.0.0 library allows attackers to cause a denial of service by providing a malformed ext4 filesystem image that results in a zero logical block size. The vulnerability is triggered during mount or image processing and leads to a Floating-Point Exception (FPE) under sanitizers or a runtime crash in standard builds due to missing validation of

Why this priority

Public exploit reference

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	5.5 (Medium)
Attack vector	Local
Attack complexity	Low
Privileges needed	None
User interaction	Required
EPSS exploit chance	0.2% (top 95%)
CISA exploited list	No
Weakness	CWE-369
Published	2026-06-03
Last modified	2026-07-22

Publisher (CNA): MITRE · Vendor: gkostka

Last updated 2026-07-22 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-06-03 14:16 UTCPublished CVE record published
2026-07-22 19:10 UTCUpdated Record last modified

gkostka lwext4 DOWNGRADE

Affected: 1.0.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 1.0.0

1. Check installed version

apt-cache policy lwext4 || rpm -q lwext4 || lwext4 --version

2. No fixed release: DOWNGRADE to a release before 1.0.0 (Debian / Ubuntu)

apt-cache madison lwext4 sudo apt install lwext4=<VERSION_BEFORE_1.0.0> sudo apt-mark hold lwext4

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list lwext4 sudo dnf downgrade lwext4-<VERSION_BEFORE_1.0.0> sudo dnf versionlock add lwext4

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2025-70100?

lwext4: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2025-70100 being exploited?

CVE-2025-70100 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2025-70100 affect?

CVE-2025-70100 affects lwext4. Severity is medium (CVSS 5.5). A divide-by-zero vulnerability in the ext4_block_set_lb_size function in src/ext4_blockdev.c of the lwext4 1.0.0 library allows attackers to cause a denial of service by providing a malformed ext4 filesystem image that results in a zero log

How urgent is CVE-2025-70100?

Priority 26/100. Public exploit reference

Related CVEs

CVE-2025-70101 MEDIUM 6.5 DOWNGRADE An out-of-bounds read in the ext4_ext_binsearch_idx function in src/ext4_extent.c of the lwext4 1.0.0 library

References

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