# CVE-2026-31423: net/sched: sch_hfsc: fix divide-by-zero in rtsc_min()

> A local attacker can cause a kernel divide-by-zero crash in the HFSC scheduler by triggering an integer truncation, leading to denial of service.

- **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:** 13 Apr 2026
- **Updated:** 15 Oct 2026
- **Also known as:** AZL-82694, BELL-CVE-2026-31423, DEBIAN-CVE-2026-31423, GHSA-mgjx-cg3q-7vjw, ROOT-OS-DEBIAN-11-CVE-2026-31423, ROOT-OS-DEBIAN-12-CVE-2026-31423, ROOT-OS-DEBIAN-13-CVE-2026-31423, ROOT-OS-UBUNTU-2204-CVE-2026-31423, ROOT-OS-UBUNTU-2404-CVE-2026-31423, UBUNTU-CVE-2026-31423

## What is CVE-2026-31423?

CVE-2026-31423 is a medium-severity vulnerability in Linux kernel, published on 13 Apr 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:

net/sched: sch_hfsc: fix divide-by-zero in rtsc_min()

m2sm() converts a u32 slope to a u64 scaled value.  For large inputs
(e.g. m1=4000000000), the result can reach 2^32.  rtsc_min() stores
the difference of two such u64 values in a u32 variable `dsm` and
uses it as a divisor.  When the difference is exactly 2^32 the
truncation yields zero, causing a divide-by-zero oops in the
concave-curve intersection path:

  Oops: divide error: 0000
  RIP: 0010:rtsc_min (net/sched/sch_hfsc.c:601)
  Call Trace:
   init_ed (net/sched/sch_hfsc.c:629)
   hfsc_enqueue (net/sched/sch_hfsc.c:1569)
   [...]

Widen `dsm` to u64 and replace do_div() with div64_u64() so the full
difference is preserved.

Weakness: CWE-369 (Divide By Zero)

## Which versions are affected by CVE-2026-31423?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-31423?

Apply the vendor's patch.

## Is CVE-2026-31423 being exploited?

There is no known exploitation of CVE-2026-31423 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-2026-31423 and fix it if it is affected.

What it is: CVE-2026-31423 is a medium-severity vulnerability in Linux kernel, published on 13 Apr 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-2026-31423 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-2026-31423/ (Markdown: https://insights.sbomify.com/CVE-2026-31423/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-31423
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-31423
- OSV: https://osv.dev/vulnerability/CVE-2026-31423

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-31423/
Summaries are generated and may contain mistakes; the official description above is the record.