# CVE-2026-90100: ptp: netc: fix period truncation and potential divide-by-zero in PEROUT

> A local attacker can trigger a divide-by-zero error in the Linux kernel NETC PTP driver, causing a system crash.

- **Severity:** Not scored
- **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:** 17 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** BELL-CVE-2026-90100, DEBIAN-CVE-2026-90100, GHSA-rpp5-w8v3-w64q, UBUNTU-CVE-2026-90100

## What is CVE-2026-90100?

CVE-2026-90100 is a vulnerability in Linux, published on 17 Sep 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:

ptp: netc: fix period truncation and potential divide-by-zero in PEROUT

The max_period bound in net_timer_enable_perout() was computed as:

  max_period = (u64)NETC_TMR_DEFAULT_FIPER + integral_period;

which exceeds U32_MAX when integral_period > 0 (e.g. 0x100000002 for
the default 333333333 Hz clock). A period_ns that passes this check but
exceeds U32_MAX is then silently truncated when stored into the u32
struct netc_pp::period field.

A truncated value of zero can reach netc_timer_set_perout_alarm(), where
the local u32 period variable would also be 0, causing a divide-by-zero
in roundup_u64(delta, period) whenever the stime < min_time branch is
taken (which always happens for a start time of {0, 0}).

Additionally, netc_timer_enable_periodic_pulse() and
netc_timer_enable_fiper() both compute:

  fiper = pp->period - integral_period;

A zero pp->period results in an unsigned wraparound to 0xFFFFFFFD,
mis-programming the FIPER hardware register.

Fix all three issues by capping max_period at NETC_TMR_DEFAULT_FIPER
(0xFFFFFFFF). This ensures that any period_ns passing the range check
fits in a u32 without truncation, so the stored value is always valid
and non-zero. The accepted range is reduced by integral_period ns
(typically only a few nanoseconds), which is negligible in practice.

## Which versions are affected by CVE-2026-90100?


## How do I fix CVE-2026-90100?

Apply the vendor's patch.

## Is CVE-2026-90100 being exploited?

There is no known exploitation of CVE-2026-90100 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-90100 and fix it if it is affected.

What it is: CVE-2026-90100 is a vulnerability in Linux, published on 17 Sep 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-2026-90100 in the wild and no public exploit code.

Affected product: Linux. 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-2026-90100/ (Markdown: https://insights.sbomify.com/CVE-2026-90100/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-90100
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-90100
- OSV: https://osv.dev/vulnerability/CVE-2026-90100

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-90100/
Summaries are generated and may contain mistakes; the official description above is the record.