# CVE-2026-80578: fbdev: core: Fix pointer desynchronization in fb_io_read()

> A pointer desynchronization bug in the Linux kernel's fbdev core allows out-of-bounds hardware reads, potentially leading to information disclosure or system crashes.

- **Severity:** High 7.3 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:L/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:** 26 Aug 2026
- **Updated:** 16 Oct 2026
- **Also known as:** AZL-97719, BELL-CVE-2026-80578, DEBIAN-CVE-2026-80578, GHSA-fvfx-mw36-f75m, UBUNTU-CVE-2026-80578

## What is CVE-2026-80578?

CVE-2026-80578 is a high-severity memory corruption vulnerability in Linux, published on 26 Aug 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: core: Fix pointer desynchronization in fb_io_read()

In fb_io_read(), if copy_to_user() performs a partial copy (e.g., due to
a faulty user buffer), the loop adjusts the chunk size 'c' and updates
the remaining 'count'. However, the hardware 'src' pointer has already
been eagerly advanced by the original chunk size.

If the loop is allowed to continue, the read will resume from an
incorrect, over-advanced offset. Since the remaining 'count' was only
decremented by the successful bytes, this desynchronization causes the
next iterations to execute more hardware reads than originally bounded,
eventually leading to out-of-bounds I/O reads.

Fix this by breaking out of the loop immediately upon a partial
copy_to_user(). A partial copy indicates a faulty user buffer, making
subsequent read attempts futile. Breaking out ensures we return the
number of successfully read bytes without risking out-of-bounds hardware
accesses in subsequent mismatched iterations.

## Which versions are affected by CVE-2026-80578?


## How do I fix CVE-2026-80578?

Apply the vendor's patch.

## Is CVE-2026-80578 being exploited?

There is no known exploitation of CVE-2026-80578 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-80578 and fix it if it is affected.

What it is: CVE-2026-80578 is a high-severity memory corruption vulnerability in Linux, published on 26 Aug 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-2026-80578 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-2026-80578/ (Markdown: https://insights.sbomify.com/CVE-2026-80578/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-80578
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-80578
- OSV: https://osv.dev/vulnerability/CVE-2026-80578

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-80578/
Summaries are generated and may contain mistakes; the official description above is the record.