CVE-2021-47641 video: fbdev: cirrusfb: check pixclock to avoid divide by zero

Medium 5.5 Published 26 Feb 2025 Updated 11 May 2026

A local attacker can cause a kernel crash via divide-by-zero in the cirrusfb driver by providing a zero pixclock value.

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-2021-47641?

CVE-2021-47641 is a medium-severity denial of service vulnerability in Linux kernel, published on 26 Feb 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:

video: fbdev: cirrusfb: check pixclock to avoid divide by zero

Do a sanity check on pixclock value to avoid divide by zero.

If the pixclock value is zero, the cirrusfb driver will round up pixclock to get the derived frequency as close to maxclock as possible.

Syzkaller reported a divide error in cirrusfb_check_pixclock.

divide error: 0000 [#1] SMP KASAN PTI CPU: 0 PID: 14938 Comm: cirrusfb_test Not tainted 5.15.0-rc6 #1 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.11.0-2 RIP: 0010:cirrusfb_check_var+0x6f1/0x1260

Call Trace: fb_set_var+0x398/0xf90 do_fb_ioctl+0x4b8/0x6f0 fb_ioctl+0xeb/0x130 __x64_sys_ioctl+0x19d/0x220 do_syscall_64+0x3a/0x80 entry_SYSCALL_64_after_hwframe+0x44/0xae

Weakness: CWE-369

Which versions are affected by CVE-2021-47641?

It affects 1 product.

Products include Linux kernel.

How do I fix CVE-2021-47641?

Apply the vendor's patch.

Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.

Is CVE-2021-47641 being exploited?

There is no known exploitation of CVE-2021-47641 in the wild and no public exploit code.

All Linux kernel vulnerabilities

Sources

Also known as DEBIAN-CVE-2021-47641, GHSA-3hf8-259h-577p, UBUNTU-CVE-2021-47641.