# CVE-2023-53642: x86: fix clear_user_rep_good() exception handling annotation

> A kernel exception handling bug causes a system crash instead of an error when clearing user memory, 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:** 7 Oct 2025
- **Updated:** 11 May 2026
- **Also known as:** BELL-CVE-2023-53642, DEBIAN-CVE-2023-53642, GHSA-h9cf-c7q8-gcqh, ROOT-OS-UBUNTU-2404-CVE-2023-53642, UBUNTU-CVE-2023-53642

## What is CVE-2023-53642?

CVE-2023-53642 is a medium-severity denial of service vulnerability in Linux kernel, published on 7 Oct 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:

x86: fix clear_user_rep_good() exception handling annotation

This code no longer exists in mainline, because it was removed in
commit d2c95f9d6802 ("x86: don't use REP_GOOD or ERMS for user memory
clearing") upstream.

However, rather than backport the full range of x86 memory clearing and
copying cleanups, fix the exception table annotation placement for the
final 'rep movsb' in clear_user_rep_good(): rather than pointing at the
actual instruction that did the user space access, it pointed to the
register move just before it.

That made sense from a code flow standpoint, but not from an actual
usage standpoint: it means that if user access takes an exception, the
exception handler won't actually find the instruction in the exception
tables.

As a result, rather than fixing it up and returning -EFAULT, it would
then turn it into a kernel oops report instead, something like:

    BUG: unable to handle page fault for address: 0000000020081000
    #PF: supervisor write access in kernel mode
    #PF: error_code(0x0002) - not-present page
    ...
    RIP: 0010:clear_user_rep_good+0x1c/0x30 arch/x86/lib/clear_page_64.S:147
    ...
    Call Trace:
      __clear_user arch/x86/include/asm/uaccess_64.h:103 [inline]
      clear_user arch/x86/include/asm/uaccess_64.h:124 [inline]
      iov_iter_zero+0x709/0x1290 lib/iov_iter.c:800
      iomap_dio_hole_iter fs/iomap/direct-io.c:389 [inline]
      iomap_dio_iter fs/iomap/direct-io.c:440 [inline]
      __iomap_dio_rw+0xe3d/0x1cd0 fs/iomap/direct-io.c:601
      iomap_dio_rw+0x40/0xa0 fs/iomap/direct-io.c:689
      ext4_dio_read_iter fs/ext4/file.c:94 [inline]
      ext4_file_read_iter+0x4be/0x690 fs/ext4/file.c:145
      call_read_iter include/linux/fs.h:2183 [inline]
      do_iter_readv_writev+0x2e0/0x3b0 fs/read_write.c:733
      do_iter_read+0x2f2/0x750 fs/read_write.c:796
      vfs_readv+0xe5/0x150 fs/read_write.c:916
      do_preadv+0x1b6/0x270 fs/read_write.c:1008
      __do_sys_preadv2 fs/read_write.c:1070 [inline]
      __se_sys_preadv2 fs/read_write.c:1061 [inline]
      __x64_sys_preadv2+0xef/0x150 fs/read_write.c:1061
      do_syscall_x64 arch/x86/entry/common.c:50 [inline]
      do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80
      entry_SYSCALL_64_after_hwframe+0x63/0xcd

which then looks like a filesystem bug rather than the incorrect
exception annotation that it is.

[ The alternative to this one-liner fix is to take the upstream series
  that cleans this all up:

    68674f94ffc9 ("x86: don't use REP_GOOD or ERMS for small memory copies")
    20f3337d350c ("x86: don't use REP_GOOD or ERMS for small memory clearing")
    adfcf4231b8c ("x86: don't use REP_GOOD or ERMS for user memory copies")
  * d2c95f9d6802 ("x86: don't use REP_GOOD or ERMS for user memory clearing")
    3639a535587d ("x86: move stac/clac from user copy routines into callers")
    577e6a7fd50d ("x86: inline the 'rep movs' in user copies for the FSRM case")
    8c9b6a88b7e2 ("x86: improve on the non-rep 'clear_user' function")
    427fda2c8a49 ("x86: improve on the non-rep 'copy_user' function")
  * e046fe5a36a9 ("x86: set FSRS automatically on AMD CPUs that have FSRM")
    e1f2750edc4a ("x86: remove 'zerorest' argument from __copy_user_nocache()")
    034ff37d3407 ("x86: rewrite '__copy_user_nocache' function")

  with either the whole series or at a minimum the two marked commits
  being needed to fix this issue ]

## Which versions are affected by CVE-2023-53642?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2023-53642?

Apply the vendor's patch.

## Is CVE-2023-53642 being exploited?

There is no known exploitation of CVE-2023-53642 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-2023-53642 and fix it if it is affected.

What it is: CVE-2023-53642 is a medium-severity denial of service vulnerability in Linux kernel, published on 7 Oct 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-2023-53642 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-2023-53642/ (Markdown: https://insights.sbomify.com/CVE-2023-53642/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2023-53642
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2023-53642
- OSV: https://osv.dev/vulnerability/CVE-2023-53642

---
From sbomify Insights: https://insights.sbomify.com/CVE-2023-53642/
Summaries are generated and may contain mistakes; the official description above is the record.