# CVE-2024-26944: btrfs: zoned: fix use-after-free in do_zone_finish()

> A use-after-free vulnerability in the Linux kernel's btrfs zoned mode allows attackers to cause a denial of service or potentially execute code.

- **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:** 1 May 2024
- **Updated:** 5 Aug 2026
- **Also known as:** AZL-55497, BELL-CVE-2024-26944, DEBIAN-CVE-2024-26944, GHSA-phc9-mf56-r5f6, ROOT-OS-DEBIAN-12-CVE-2024-26944, UBUNTU-CVE-2024-26944

## What is CVE-2024-26944?

CVE-2024-26944 is a high-severity use after free vulnerability in Linux kernel, published on 1 May 2024. 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:

btrfs: zoned: fix use-after-free in do_zone_finish()

Shinichiro reported the following use-after-free triggered by the device
replace operation in fstests btrfs/070.

 BTRFS info (device nullb1): scrub: finished on devid 1 with status: 0
 ==================================================================
 BUG: KASAN: slab-use-after-free in do_zone_finish+0x91a/0xb90 [btrfs]
 Read of size 8 at addr ffff8881543c8060 by task btrfs-cleaner/3494007

 CPU: 0 PID: 3494007 Comm: btrfs-cleaner Tainted: G        W          6.8.0-rc5-kts #1
 Hardware name: Supermicro Super Server/X11SPi-TF, BIOS 3.3 02/21/2020
 Call Trace:
  <TASK>
  dump_stack_lvl+0x5b/0x90
  print_report+0xcf/0x670
  ? __virt_addr_valid+0x200/0x3e0
  kasan_report+0xd8/0x110
  ? do_zone_finish+0x91a/0xb90 [btrfs]
  ? do_zone_finish+0x91a/0xb90 [btrfs]
  do_zone_finish+0x91a/0xb90 [btrfs]
  btrfs_delete_unused_bgs+0x5e1/0x1750 [btrfs]
  ? __pfx_btrfs_delete_unused_bgs+0x10/0x10 [btrfs]
  ? btrfs_put_root+0x2d/0x220 [btrfs]
  ? btrfs_clean_one_deleted_snapshot+0x299/0x430 [btrfs]
  cleaner_kthread+0x21e/0x380 [btrfs]
  ? __pfx_cleaner_kthread+0x10/0x10 [btrfs]
  kthread+0x2e3/0x3c0
  ? __pfx_kthread+0x10/0x10
  ret_from_fork+0x31/0x70
  ? __pfx_kthread+0x10/0x10
  ret_from_fork_asm+0x1b/0x30
  </TASK>

 Allocated by task 3493983:
  kasan_save_stack+0x33/0x60
  kasan_save_track+0x14/0x30
  __kasan_kmalloc+0xaa/0xb0
  btrfs_alloc_device+0xb3/0x4e0 [btrfs]
  device_list_add.constprop.0+0x993/0x1630 [btrfs]
  btrfs_scan_one_device+0x219/0x3d0 [btrfs]
  btrfs_control_ioctl+0x26e/0x310 [btrfs]
  __x64_sys_ioctl+0x134/0x1b0
  do_syscall_64+0x99/0x190
  entry_SYSCALL_64_after_hwframe+0x6e/0x76

 Freed by task 3494056:
  kasan_save_stack+0x33/0x60
  kasan_save_track+0x14/0x30
  kasan_save_free_info+0x3f/0x60
  poison_slab_object+0x102/0x170
  __kasan_slab_free+0x32/0x70
  kfree+0x11b/0x320
  btrfs_rm_dev_replace_free_srcdev+0xca/0x280 [btrfs]
  btrfs_dev_replace_finishing+0xd7e/0x14f0 [btrfs]
  btrfs_dev_replace_by_ioctl+0x1286/0x25a0 [btrfs]
  btrfs_ioctl+0xb27/0x57d0 [btrfs]
  __x64_sys_ioctl+0x134/0x1b0
  do_syscall_64+0x99/0x190
  entry_SYSCALL_64_after_hwframe+0x6e/0x76

 The buggy address belongs to the object at ffff8881543c8000
  which belongs to the cache kmalloc-1k of size 1024
 The buggy address is located 96 bytes inside of
  freed 1024-byte region [ffff8881543c8000, ffff8881543c8400)

 The buggy address belongs to the physical page:
 page:00000000fe2c1285 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x1543c8
 head:00000000fe2c1285 order:3 entire_mapcount:0 nr_pages_mapped:0 pincount:0
 flags: 0x17ffffc0000840(slab|head|node=0|zone=2|lastcpupid=0x1fffff)
 page_type: 0xffffffff()
 raw: 0017ffffc0000840 ffff888100042dc0 ffffea0019e8f200 dead000000000002
 raw: 0000000000000000 0000000000100010 00000001ffffffff 0000000000000000
 page dumped because: kasan: bad access detected

 Memory state around the buggy address:
  ffff8881543c7f00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  ffff8881543c7f80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 >ffff8881543c8000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                                        ^
  ffff8881543c8080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
  ffff8881543c8100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb

This UAF happens because we're accessing stale zone information of a
already removed btrfs_device in do_zone_finish().

The sequence of events is as follows:

btrfs_dev_replace_start
  btrfs_scrub_dev
   btrfs_dev_replace_finishing
    btrfs_dev_replace_update_device_in_mapping_tree <-- devices replaced
    btrfs_rm_dev_replace_free_srcdev
     btrfs_free_device                              <-- device freed

cleaner_kthread
 btrfs_delete_unused_bgs
  btrfs_zone_finish
   do_zone_finish              <-- refers the freed device

The reason for this is that we're using a
---truncated---

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2024-26944?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2024-26944?

Apply the vendor's patch.

## Is CVE-2024-26944 being exploited?

There is no known exploitation of CVE-2024-26944 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-2024-26944 and fix it if it is affected.

What it is: CVE-2024-26944 is a high-severity use after free vulnerability in Linux kernel, published on 1 May 2024. 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-2024-26944 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-2024-26944/ (Markdown: https://insights.sbomify.com/CVE-2024-26944/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2024-26944
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2024-26944
- OSV: https://osv.dev/vulnerability/CVE-2024-26944

---
From sbomify Insights: https://insights.sbomify.com/CVE-2024-26944/
Summaries are generated and may contain mistakes; the official description above is the record.