# CVE-2026-23266: fbdev: rivafb: fix divide error in nv3_arb()

> A local attacker can crash the Linux kernel by triggering a divide-by-zero error in the rivafb driver via a crafted ioctl call.

- **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:** 18 Mar 2026
- **Updated:** 11 May 2026
- **Also known as:** AZL-80097, BELL-CVE-2026-23266, DEBIAN-CVE-2026-23266, GHSA-c589-8xvr-7cm3, ROOT-OS-UBUNTU-2204-CVE-2026-23266, ROOT-OS-UBUNTU-2404-CVE-2026-23266, UBUNTU-CVE-2026-23266

## What is CVE-2026-23266?

CVE-2026-23266 is a medium-severity denial of service vulnerability in Linux kernel, published on 18 Mar 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:

fbdev: rivafb: fix divide error in nv3_arb()

A userspace program can trigger the RIVA NV3 arbitration code by calling
the FBIOPUT_VSCREENINFO ioctl on /dev/fb*. When doing so, the driver
recomputes FIFO arbitration parameters in nv3_arb(), using state->mclk_khz
(derived from the PRAMDAC MCLK PLL) as a divisor without validating it
first.

In a normal setup, state->mclk_khz is provided by the real hardware and is
non-zero. However, an attacker can construct a malicious or misconfigured
device (e.g. a crafted/emulated PCI device) that exposes a bogus PLL
configuration, causing state->mclk_khz to become zero.  Once
nv3_get_param() calls nv3_arb(), the division by state->mclk_khz in the gns
calculation causes a divide error and crashes the kernel.

Fix this by checking whether state->mclk_khz is zero and bailing out before
doing the division.

The following log reveals it:

rivafb: setting virtual Y resolution to 2184
divide error: 0000 [#1] PREEMPT SMP KASAN PTI
CPU: 0 PID: 2187 Comm: syz-executor.0 Not tainted 5.18.0-rc1+ #1
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.12.0-59-gc9ba5276e321-prebuilt.qemu.org 04/01/2014
RIP: 0010:nv3_arb drivers/video/fbdev/riva/riva_hw.c:439 [inline]
RIP: 0010:nv3_get_param+0x3ab/0x13b0 drivers/video/fbdev/riva/riva_hw.c:546
Call Trace:
  nv3CalcArbitration.constprop.0+0x255/0x460 drivers/video/fbdev/riva/riva_hw.c:603
  nv3UpdateArbitrationSettings drivers/video/fbdev/riva/riva_hw.c:637 [inline]
  CalcStateExt+0x447/0x1b90 drivers/video/fbdev/riva/riva_hw.c:1246
  riva_load_video_mode+0x8a9/0xea0 drivers/video/fbdev/riva/fbdev.c:779
  rivafb_set_par+0xc0/0x5f0 drivers/video/fbdev/riva/fbdev.c:1196
  fb_set_var+0x604/0xeb0 drivers/video/fbdev/core/fbmem.c:1033
  do_fb_ioctl+0x234/0x670 drivers/video/fbdev/core/fbmem.c:1109
  fb_ioctl+0xdd/0x130 drivers/video/fbdev/core/fbmem.c:1188
  __x64_sys_ioctl+0x122/0x190 fs/ioctl.c:856

Weakness: CWE-369 (Divide By Zero)

## Which versions are affected by CVE-2026-23266?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-23266?

Apply the vendor's patch.

## Is CVE-2026-23266 being exploited?

There is no known exploitation of CVE-2026-23266 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-2026-23266 and fix it if it is affected.

What it is: CVE-2026-23266 is a medium-severity denial of service vulnerability in Linux kernel, published on 18 Mar 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-2026-23266 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-2026-23266/ (Markdown: https://insights.sbomify.com/CVE-2026-23266/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-23266
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-23266
- OSV: https://osv.dev/vulnerability/CVE-2026-23266

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-23266/
Summaries are generated and may contain mistakes; the official description above is the record.