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

Medium 5.5 Published 14 Feb 2026 Updated 19 Oct 2026

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

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

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

Which versions are affected by CVE-2026-23121?

It affects 1 product.

Products include 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.

All Linux kernel vulnerabilities

Sources

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 and 1 more.