# CVE-2022-50021: ext4: block range must be validated before use in ext4_mb_clear_bb()

> A local attacker can cause a kernel crash by mounting a corrupted ext4 filesystem with bigalloc enabled, leading to denial of service.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/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:** 18 Jun 2025
- **Updated:** 11 May 2026
- **Also known as:** DEBIAN-CVE-2022-50021, GHSA-h5r3-g6g9-3w6p, UBUNTU-CVE-2022-50021

## What is CVE-2022-50021?

CVE-2022-50021 is a high-severity use after free vulnerability in Linux kernel, published on 18 Jun 2025. 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: block range must be validated before use in ext4_mb_clear_bb()

Block range to free is validated in ext4_free_blocks() using
ext4_inode_block_valid() and then it's passed to ext4_mb_clear_bb().
However in some situations on bigalloc file system the range might be
adjusted after the validation in ext4_free_blocks() which can lead to
troubles on corrupted file systems such as one found by syzkaller that
resulted in the following BUG

kernel BUG at fs/ext4/ext4.h:3319!
PREEMPT SMP NOPTI
CPU: 28 PID: 4243 Comm: repro Kdump: loaded Not tainted 5.19.0-rc6+ #1
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.15.0-1.fc35 04/01/2014
RIP: 0010:ext4_free_blocks+0x95e/0xa90
Call Trace:
 <TASK>
 ? lock_timer_base+0x61/0x80
 ? __es_remove_extent+0x5a/0x760
 ? __mod_timer+0x256/0x380
 ? ext4_ind_truncate_ensure_credits+0x90/0x220
 ext4_clear_blocks+0x107/0x1b0
 ext4_free_data+0x15b/0x170
 ext4_ind_truncate+0x214/0x2c0
 ? _raw_spin_unlock+0x15/0x30
 ? ext4_discard_preallocations+0x15a/0x410
 ? ext4_journal_check_start+0xe/0x90
 ? __ext4_journal_start_sb+0x2f/0x110
 ext4_truncate+0x1b5/0x460
 ? __ext4_journal_start_sb+0x2f/0x110
 ext4_evict_inode+0x2b4/0x6f0
 evict+0xd0/0x1d0
 ext4_enable_quotas+0x11f/0x1f0
 ext4_orphan_cleanup+0x3de/0x430
 ? proc_create_seq_private+0x43/0x50
 ext4_fill_super+0x295f/0x3ae0
 ? snprintf+0x39/0x40
 ? sget_fc+0x19c/0x330
 ? ext4_reconfigure+0x850/0x850
 get_tree_bdev+0x16d/0x260
 vfs_get_tree+0x25/0xb0
 path_mount+0x431/0xa70
 __x64_sys_mount+0xe2/0x120
 do_syscall_64+0x5b/0x80
 ? do_user_addr_fault+0x1e2/0x670
 ? exc_page_fault+0x70/0x170
 entry_SYSCALL_64_after_hwframe+0x46/0xb0
RIP: 0033:0x7fdf4e512ace

Fix it by making sure that the block range is properly validated before
used every time it changes in ext4_free_blocks() or ext4_mb_clear_bb().

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2022-50021?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2022-50021?

Apply the vendor's patch.

## Is CVE-2022-50021 being exploited?

There is no known exploitation of CVE-2022-50021 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-2022-50021 and fix it if it is affected.

What it is: CVE-2022-50021 is a high-severity use after free vulnerability in Linux kernel, published on 18 Jun 2025. 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-2022-50021 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-2022-50021/ (Markdown: https://insights.sbomify.com/CVE-2022-50021/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2022-50021
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2022-50021
- OSV: https://osv.dev/vulnerability/CVE-2022-50021

---
From sbomify Insights: https://insights.sbomify.com/CVE-2022-50021/
Summaries are generated and may contain mistakes; the official description above is the record.