# CVE-2026-23121: mISDN: annotate data-race around dev->work

> A data race in the Linux kernel mISDN driver can lead to undefined behavior, requiring kernel patching to ensure thread safety.

- **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:** 14 Feb 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-77793, BELL-CVE-2026-23121, DEBIAN-CVE-2026-23121, GHSA-h3v4-524h-5jpx, ROOT-OS-UBUNTU-2204-CVE-2026-23121, ROOT-OS-UBUNTU-2404-CVE-2026-23121, UBUNTU-CVE-2026-23121

## What is CVE-2026-23121?

CVE-2026-23121 is a medium-severity vulnerability in Linux kernel, published on 14 Feb 2026. 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:

mISDN: annotate data-race around dev->work

dev->work can re read locklessly in mISDN_read()
and mISDN_poll(). Add READ_ONCE()/WRITE_ONCE() annotations.

BUG: KCSAN: data-race in mISDN_ioctl / mISDN_read

write to 0xffff88812d848280 of 4 bytes by task 10864 on cpu 1:
  misdn_add_timer drivers/isdn/mISDN/timerdev.c:175 [inline]
  mISDN_ioctl+0x2fb/0x550 drivers/isdn/mISDN/timerdev.c:233
  vfs_ioctl fs/ioctl.c:51 [inline]
  __do_sys_ioctl fs/ioctl.c:597 [inline]
  __se_sys_ioctl+0xce/0x140 fs/ioctl.c:583
  __x64_sys_ioctl+0x43/0x50 fs/ioctl.c:583
  x64_sys_call+0x14b0/0x3000 arch/x86/include/generated/asm/syscalls_64.h:17
  do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
  do_syscall_64+0xd8/0x2c0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88812d848280 of 4 bytes by task 10857 on cpu 0:
  mISDN_read+0x1f2/0x470 drivers/isdn/mISDN/timerdev.c:112
  do_loop_readv_writev fs/read_write.c:847 [inline]
  vfs_readv+0x3fb/0x690 fs/read_write.c:1020
  do_readv+0xe7/0x210 fs/read_write.c:1080
  __do_sys_readv fs/read_write.c:1165 [inline]
  __se_sys_readv fs/read_write.c:1162 [inline]
  __x64_sys_readv+0x45/0x50 fs/read_write.c:1162
  x64_sys_call+0x2831/0x3000 arch/x86/include/generated/asm/syscalls_64.h:20
  do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
  do_syscall_64+0xd8/0x2c0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x00000000 -> 0x00000001

Weakness: CWE-362 (Concurrent Execution using Shared Resource with Improper Synchronization)

## Which versions are affected by CVE-2026-23121?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-23121?

Apply the vendor's patch.

## Is CVE-2026-23121 being exploited?

There is no known exploitation of CVE-2026-23121 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-2026-23121 and fix it if it is affected.

What it is: CVE-2026-23121 is a medium-severity vulnerability in Linux kernel, published on 14 Feb 2026. 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-2026-23121 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-2026-23121/ (Markdown: https://insights.sbomify.com/CVE-2026-23121/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-23121
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-23121
- OSV: https://osv.dev/vulnerability/CVE-2026-23121

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-23121/
Summaries are generated and may contain mistakes; the official description above is the record.