# CVE-2024-56693: brd: defer automatic disk creation until module initialization succeeds

> A use-after-free vulnerability in the Linux kernel brd driver allows local attackers to cause a system crash or potentially execute code during module initialization failures.

- **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:** 28 Dec 2024
- **Updated:** 5 Aug 2026
- **Also known as:** BELL-CVE-2024-56693, DEBIAN-CVE-2024-56693, GHSA-mh6m-gjcw-57ph, UBUNTU-CVE-2024-56693

## What is CVE-2024-56693?

CVE-2024-56693 is a high-severity use after free vulnerability in Linux kernel, published on 28 Dec 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:

brd: defer automatic disk creation until module initialization succeeds

My colleague Wupeng found the following problems during fault injection:

BUG: unable to handle page fault for address: fffffbfff809d073
PGD 6e648067 P4D 123ec8067 PUD 123ec4067 PMD 100e38067 PTE 0
Oops: Oops: 0000 [#1] PREEMPT SMP KASAN NOPTI
CPU: 5 UID: 0 PID: 755 Comm: modprobe Not tainted 6.12.0-rc3+ #17
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
1.16.1-2.fc37 04/01/2014
RIP: 0010:__asan_load8+0x4c/0xa0
...
Call Trace:
 <TASK>
 blkdev_put_whole+0x41/0x70
 bdev_release+0x1a3/0x250
 blkdev_release+0x11/0x20
 __fput+0x1d7/0x4a0
 task_work_run+0xfc/0x180
 syscall_exit_to_user_mode+0x1de/0x1f0
 do_syscall_64+0x6b/0x170
 entry_SYSCALL_64_after_hwframe+0x76/0x7e

loop_init() is calling loop_add() after __register_blkdev() succeeds and
is ignoring disk_add() failure from loop_add(), for loop_add() failure
is not fatal and successfully created disks are already visible to
bdev_open().

brd_init() is currently calling brd_alloc() before __register_blkdev()
succeeds and is releasing successfully created disks when brd_init()
returns an error. This can cause UAF for the latter two case:

case 1:
    T1:
modprobe brd
  brd_init
    brd_alloc(0) // success
      add_disk
        disk_scan_partitions
          bdev_file_open_by_dev // alloc file
          fput // won't free until back to userspace
    brd_alloc(1) // failed since mem alloc error inject
  // error path for modprobe will release code segment
  // back to userspace
  __fput
    blkdev_release
      bdev_release
        blkdev_put_whole
          bdev->bd_disk->fops->release // fops is freed now, UAF!

case 2:
    T1:                            T2:
modprobe brd
  brd_init
    brd_alloc(0) // success
                                   open(/dev/ram0)
    brd_alloc(1) // fail
  // error path for modprobe

                                   close(/dev/ram0)
                                   ...
                                   /* UAF! */
                                   bdev->bd_disk->fops->release

Fix this problem by following what loop_init() does. Besides,
reintroduce brd_devices_mutex to help serialize modifications to
brd_list.

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2024-56693?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2024-56693?

Apply the vendor's patch.

## Is CVE-2024-56693 being exploited?

There is no known exploitation of CVE-2024-56693 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-2024-56693 and fix it if it is affected.

What it is: CVE-2024-56693 is a high-severity use after free vulnerability in Linux kernel, published on 28 Dec 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-2024-56693 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-2024-56693/ (Markdown: https://insights.sbomify.com/CVE-2024-56693/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2024-56693
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2024-56693
- OSV: https://osv.dev/vulnerability/CVE-2024-56693

---
From sbomify Insights: https://insights.sbomify.com/CVE-2024-56693/
Summaries are generated and may contain mistakes; the official description above is the record.