# CVE-2024-53171: ubifs: authentication: Fix use-after-free in ubifs_tnc_end_commit

> A use-after-free in the Linux kernel UBIFS authentication module allows local attackers to cause a crash 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:** 27 Dec 2024
- **Updated:** 5 Aug 2026
- **Also known as:** BELL-CVE-2024-53171, DEBIAN-CVE-2024-53171, GHSA-2gwr-frhx-j93x, UBUNTU-CVE-2024-53171

## What is CVE-2024-53171?

CVE-2024-53171 is a high-severity use after free vulnerability in Linux kernel, published on 27 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:

ubifs: authentication: Fix use-after-free in ubifs_tnc_end_commit

After an insertion in TNC, the tree might split and cause a node to
change its `znode->parent`. A further deletion of other nodes in the
tree (which also could free the nodes), the aforementioned node's
`znode->cparent` could still point to a freed node. This
`znode->cparent` may not be updated when getting nodes to commit in
`ubifs_tnc_start_commit()`. This could then trigger a use-after-free
when accessing the `znode->cparent` in `write_index()` in
`ubifs_tnc_end_commit()`.

This can be triggered by running

  rm -f /etc/test-file.bin
  dd if=/dev/urandom of=/etc/test-file.bin bs=1M count=60 conv=fsync

in a loop, and with `CONFIG_UBIFS_FS_AUTHENTICATION`. KASAN then
reports:

  BUG: KASAN: use-after-free in ubifs_tnc_end_commit+0xa5c/0x1950
  Write of size 32 at addr ffffff800a3af86c by task ubifs_bgt0_20/153

  Call trace:
   dump_backtrace+0x0/0x340
   show_stack+0x18/0x24
   dump_stack_lvl+0x9c/0xbc
   print_address_description.constprop.0+0x74/0x2b0
   kasan_report+0x1d8/0x1f0
   kasan_check_range+0xf8/0x1a0
   memcpy+0x84/0xf4
   ubifs_tnc_end_commit+0xa5c/0x1950
   do_commit+0x4e0/0x1340
   ubifs_bg_thread+0x234/0x2e0
   kthread+0x36c/0x410
   ret_from_fork+0x10/0x20

  Allocated by task 401:
   kasan_save_stack+0x38/0x70
   __kasan_kmalloc+0x8c/0xd0
   __kmalloc+0x34c/0x5bc
   tnc_insert+0x140/0x16a4
   ubifs_tnc_add+0x370/0x52c
   ubifs_jnl_write_data+0x5d8/0x870
   do_writepage+0x36c/0x510
   ubifs_writepage+0x190/0x4dc
   __writepage+0x58/0x154
   write_cache_pages+0x394/0x830
   do_writepages+0x1f0/0x5b0
   filemap_fdatawrite_wbc+0x170/0x25c
   file_write_and_wait_range+0x140/0x190
   ubifs_fsync+0xe8/0x290
   vfs_fsync_range+0xc0/0x1e4
   do_fsync+0x40/0x90
   __arm64_sys_fsync+0x34/0x50
   invoke_syscall.constprop.0+0xa8/0x260
   do_el0_svc+0xc8/0x1f0
   el0_svc+0x34/0x70
   el0t_64_sync_handler+0x108/0x114
   el0t_64_sync+0x1a4/0x1a8

  Freed by task 403:
   kasan_save_stack+0x38/0x70
   kasan_set_track+0x28/0x40
   kasan_set_free_info+0x28/0x4c
   __kasan_slab_free+0xd4/0x13c
   kfree+0xc4/0x3a0
   tnc_delete+0x3f4/0xe40
   ubifs_tnc_remove_range+0x368/0x73c
   ubifs_tnc_remove_ino+0x29c/0x2e0
   ubifs_jnl_delete_inode+0x150/0x260
   ubifs_evict_inode+0x1d4/0x2e4
   evict+0x1c8/0x450
   iput+0x2a0/0x3c4
   do_unlinkat+0x2cc/0x490
   __arm64_sys_unlinkat+0x90/0x100
   invoke_syscall.constprop.0+0xa8/0x260
   do_el0_svc+0xc8/0x1f0
   el0_svc+0x34/0x70
   el0t_64_sync_handler+0x108/0x114
   el0t_64_sync+0x1a4/0x1a8

The offending `memcpy()` in `ubifs_copy_hash()` has a use-after-free
when a node becomes root in TNC but still has a `cparent` to an already
freed node. More specifically, consider the following TNC:

         zroot
         /
        /
      zp1
      /
     /
    zn

Inserting a new node `zn_new` with a key smaller then `zn` will trigger
a split in `tnc_insert()` if `zp1` is full:

         zroot
         /   \
        /     \
      zp1     zp2
      /         \
     /           \
  zn_new          zn

`zn->parent` has now been moved to `zp2`, *but* `zn->cparent` still
points to `zp1`.

Now, consider a removal of all the nodes _except_ `zn`. Just when
`tnc_delete()` is about to delete `zroot` and `zp2`:

         zroot
             \
              \
              zp2
                \
                 \
                 zn

`zroot` and `zp2` get freed and the tree collapses:

           zn

`zn` now becomes the new `zroot`.

`get_znodes_to_commit()` will now only find `zn`, the new `zroot`, and
`write_index()` will check its `znode->cparent` that wrongly points to
the already freed `zp1`. `ubifs_copy_hash()` thus gets wrongly called
with `znode->cparent->zbranch[znode->iip].hash` that triggers the
use-after-free!

Fix this by explicitly setting `znode->cparent` to `NULL` in
`get_znodes_to_commit()` for the root node. The search for the dirty
nodes
---truncated---

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2024-53171?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2024-53171?

Apply the vendor's patch.

## Is CVE-2024-53171 being exploited?

There is no known exploitation of CVE-2024-53171 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-2024-53171 and fix it if it is affected.

What it is: CVE-2024-53171 is a high-severity use after free vulnerability in Linux kernel, published on 27 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-2024-53171 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-2024-53171/ (Markdown: https://insights.sbomify.com/CVE-2024-53171/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2024-53171
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2024-53171
- OSV: https://osv.dev/vulnerability/CVE-2024-53171

---
From sbomify Insights: https://insights.sbomify.com/CVE-2024-53171/
Summaries are generated and may contain mistakes; the official description above is the record.