# CVE-2026-80876: ring-buffer: Fix event length with forced 8-byte alignment

> A flaw in the Linux kernel ring buffer causes incorrect length reporting for small events on specific architectures, potentially leading to information disclosure.

- **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:** 4 Sep 2026
- **Updated:** 4 Sep 2026
- **Also known as:** BELL-CVE-2026-80876, DEBIAN-CVE-2026-80876, GHSA-f6hv-xhx3-9x64, UBUNTU-CVE-2026-80876

## What is CVE-2026-80876?

CVE-2026-80876 is a vulnerability in Linux, published on 4 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:

ring-buffer: Fix event length with forced 8-byte alignment

When RB_FORCE_8BYTE_ALIGNMENT is true, rb_calculate_event_length()
reserves the space of event->array[0] for placing the data length and
rb_update_event() stores the data length in event->array[0]
accordingly. As a result the whole event length will add extra 4 bytes
for sizeof(event.array[0]) unconditionally.

But ring_buffer_event_length() only subtracts the
sizeof(event->array[0]) for events larger than RB_MAX_SMALL_DATA +
sizeof(event->array[0]). As a result, small events on architectures
with RB_FORCE_8BYTE_ALIGNMENT=true report a data length that is 4
bytes larger than expected.

To fix it, add the RB_FORCE_8BYTE_ALIGNMENT as a condition to subtract
the size of that length field whenever RB_FORCE_8BYTE_ALIGNMENT is
true.

This issue is observed in a riscv64 kernel with
CONFIG_HAVE_64BIT_ALIGNED_ACCESS set to y, when we run ftrace selftest
trace_marker_raw.tc, we get the weird log: for cases where the id is
1..100, the number of data field is 8*N, but once id exceeds 100, the
number of data field becomes 8*N+4:
 # 1 buf: 58 00 00 00 80 5e d1 63 (number of data field is 8*1)
 ...
 # a buf: 58 ...                  (number of data field is 8*2)
 ...
 # 64 buf: 58 ...                 (number of data field is 8*13)
 # 65 buf: 58 ...                 (number of data field is 8*13+4)

After applying this change, the number of data field keeps being 8*N+4
consistently.

## Which versions are affected by CVE-2026-80876?


## How do I fix CVE-2026-80876?

Apply the vendor's patch.

## Is CVE-2026-80876 being exploited?

There is no known exploitation of CVE-2026-80876 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-80876 and fix it if it is affected.

What it is: CVE-2026-80876 is a vulnerability in Linux, published on 4 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-2026-80876 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-2026-80876/ (Markdown: https://insights.sbomify.com/CVE-2026-80876/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-80876
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-80876
- OSV: https://osv.dev/vulnerability/CVE-2026-80876

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-80876/
Summaries are generated and may contain mistakes; the official description above is the record.