# CVE-2026-98848: rtc: ac100: Assign .num before accessing .hws

> A missing initialization in the Linux kernel AC100 RTC driver causes a bounds sanitizer trap during probe, leading to a local denial of service.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 18 Oct 2026
- **Updated:** 21 Oct 2026
- **Also known as:** AZL-109458, BELL-CVE-2026-98848, DEBIAN-CVE-2026-98848, GHSA-hf5g-mj3f-66c7, UBUNTU-CVE-2026-98848

## What is CVE-2026-98848?

CVE-2026-98848 is a denial of service vulnerability in Linux, published on 18 Oct 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:

rtc: ac100: Assign .num before accessing .hws

Commit f316cdff8d67 ("clk: Annotate struct clk_hw_onecell_data with
__counted_by") annotated the hws member of 'struct clk_hw_onecell_data'
with __counted_by, which informs the bounds sanitizer (UBSAN_BOUNDS)
about the number of elements in .hws[], so that it can warn when .hws[]
is accessed out of bounds. As noted in that change, the __counted_by
member must be initialized with the number of elements before the first
array access happens, otherwise there will be a warning from each access
prior to the initialization because the number of elements is zero.
This occurs in ac100_rtc_register_clks() due to .num being assigned only
after every clkout clock has been stored in .hws[]. With
CONFIG_UBSAN_BOUNDS and a compiler that implements __counted_by (GCC
15.1+ or Clang 20.1+), this triggers an array-index-out-of-bounds report
during probe, and with CONFIG_UBSAN_TRAP the first store traps.

Initialize .num with AC100_CLKOUT_NUM, the number of elements .hws[] was
allocated with, right after the allocation. That is the value the loop
counter ends up at on the success path anyway, so the provider's
behaviour is unchanged.

## Which versions are affected by CVE-2026-98848?


## How do I fix CVE-2026-98848?

Apply the vendor's patch.

## Is CVE-2026-98848 being exploited?

There is no known exploitation of CVE-2026-98848 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98848 and fix it if it is affected.

What it is: CVE-2026-98848 is a denial of service vulnerability in Linux, published on 18 Oct 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-2026-98848 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-2026-98848/ (Markdown: https://insights.sbomify.com/CVE-2026-98848/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98848
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98848
- OSV: https://osv.dev/vulnerability/CVE-2026-98848

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98848/
Summaries are generated and may contain mistakes; the official description above is the record.