# CVE-2026-43288: ext4: move ext4_percpu_param_init() before ext4_mb_init()

> A local attacker can cause a kernel panic in the ext4 filesystem by mounting a crafted image with specific quota options, leading to denial of service.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 8 May 2026
- **Updated:** 14 Sep 2026
- **Also known as:** BELL-CVE-2026-43288, DEBIAN-CVE-2026-43288, GHSA-h57h-m4cv-vwxg, ROOT-OS-DEBIAN-11-CVE-2026-43288, ROOT-OS-DEBIAN-12-CVE-2026-43288, ROOT-OS-UBUNTU-2204-CVE-2026-43288, ROOT-OS-UBUNTU-2404-CVE-2026-43288, UBUNTU-CVE-2026-43288

## What is CVE-2026-43288?

CVE-2026-43288 is a medium-severity vulnerability in Linux kernel, published on 8 May 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

ext4: move ext4_percpu_param_init() before ext4_mb_init()

When running `kvm-xfstests -c ext4/1k -C 1 generic/383` with the
`DOUBLE_CHECK` macro defined, the following panic is triggered:

==================================================================
EXT4-fs error (device vdc): ext4_validate_block_bitmap:423:
                        comm mount: bg 0: bad block bitmap checksum
BUG: unable to handle page fault for address: ff110000fa2cc000
PGD 3e01067 P4D 3e02067 PUD 0
Oops: Oops: 0000 [#1] SMP NOPTI
CPU: 0 UID: 0 PID: 2386 Comm: mount Tainted: G W
                        6.18.0-gba65a4e7120a-dirty #1152 PREEMPT(none)
RIP: 0010:percpu_counter_add_batch+0x13/0xa0
Call Trace:
 <TASK>
 ext4_mark_group_bitmap_corrupted+0xcb/0xe0
 ext4_validate_block_bitmap+0x2a1/0x2f0
 ext4_read_block_bitmap+0x33/0x50
 mb_group_bb_bitmap_alloc+0x33/0x80
 ext4_mb_add_groupinfo+0x190/0x250
 ext4_mb_init_backend+0x87/0x290
 ext4_mb_init+0x456/0x640
 __ext4_fill_super+0x1072/0x1680
 ext4_fill_super+0xd3/0x280
 get_tree_bdev_flags+0x132/0x1d0
 vfs_get_tree+0x29/0xd0
 vfs_cmd_create+0x59/0xe0
 __do_sys_fsconfig+0x4f6/0x6b0
 do_syscall_64+0x50/0x1f0
 entry_SYSCALL_64_after_hwframe+0x76/0x7e
==================================================================

This issue can be reproduced using the following commands:
        mkfs.ext4 -F -q -b 1024 /dev/sda 5G
        tune2fs -O quota,project /dev/sda
        mount /dev/sda /tmp/test

With DOUBLE_CHECK defined, mb_group_bb_bitmap_alloc() reads
and validates the block bitmap. When the validation fails,
ext4_mark_group_bitmap_corrupted() attempts to update
sbi->s_freeclusters_counter. However, this percpu_counter has not been
initialized yet at this point, which leads to the panic described above.

Fix this by moving the execution of ext4_percpu_param_init() to occur
before ext4_mb_init(), ensuring the per-CPU counters are initialized
before they are used.

Weakness: CWE-908 (Use of Uninitialized Resource)

## Which versions are affected by CVE-2026-43288?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-43288?

Apply the vendor's patch.

## Is CVE-2026-43288 being exploited?

There is no known exploitation of CVE-2026-43288 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-43288 and fix it if it is affected.

What it is: CVE-2026-43288 is a medium-severity vulnerability in Linux kernel, published on 8 May 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-2026-43288 in the wild and no public exploit code.

Affected product: Linux kernel. 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-2026-43288/ (Markdown: https://insights.sbomify.com/CVE-2026-43288/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-43288
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-43288
- OSV: https://osv.dev/vulnerability/CVE-2026-43288

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-43288/
Summaries are generated and may contain mistakes; the official description above is the record.