CVE-2026-43067 ext4: handle wraparound when searching for blocks for indirect mapped blocks
An integer wraparound in ext4 block allocation allows attackers to read or modify data outside intended bounds on indirect-mapped files.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-43067?
CVE-2026-43067 is a critical vulnerability in Linux kernel, published on 5 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
ext4: handle wraparound when searching for blocks for indirect mapped blocks
Commit 4865c768b563 ("ext4: always allocate blocks only from groups inode can use") restricts what blocks will be allocated for indirect block based files to block numbers that fit within 32-bit block numbers.
However, when using a review bot running on the latest Gemini LLM to check this commit when backporting into an LTS based kernel, it raised this concern:
If ac->ac_g_ex.fe_group is >= ngroups (for instance, if the goal group was populated via stream allocation from s_mb_last_groups), then start will be >= ngroups.
Does this allow allocating blocks beyond the 32-bit limit for indirect block mapped files? The commit message mentions that ext4_mb_scan_groups_linear() takes care to not select unsupported groups. However, its loop uses group = *start, and the very first iteration will call ext4_mb_scan_group() with this unsupported group because next_linear_group() is only called at the end of the iteration.
After reviewing the code paths involved and considering the LLM review, I determined that this can happen when there is a file system where some files/directories are extent-mapped and others are indirect-block mapped. To address this, add a safety clamp in ext4_mb_scan_groups().
Weakness: CWE-822
Which versions are affected by CVE-2026-43067?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-43067?
Apply the vendor's patch.
Is CVE-2026-43067 being exploited?
There is no known exploitation of CVE-2026-43067 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2026-43067, DEBIAN-CVE-2026-43067, GHSA-845x-q62g-4v8p, UBUNTU-CVE-2026-43067.