# CVE-2026-63826: fbdev: fix use-after-free in store_modes()

> A use-after-free in the Linux kernel fbdev subsystem allows local attackers to execute arbitrary code or escalate privileges via crafted ioctl calls.

- **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:** 19 Jul 2026
- **Updated:** 17 Aug 2026
- **Also known as:** AZL-92579, BELL-CVE-2026-63826, DEBIAN-CVE-2026-63826, GHSA-qmc7-p94r-m2hm, ROOT-OS-DEBIAN-11-CVE-2026-63826, ROOT-OS-DEBIAN-12-CVE-2026-63826, ROOT-OS-UBUNTU-2204-CVE-2026-63826, UBUNTU-CVE-2026-63826

## What is CVE-2026-63826?

CVE-2026-63826 is an use after free vulnerability in Linux, published on 19 Jul 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: fix use-after-free in store_modes()

store_modes() replaces a framebuffer's modelist with modes from userspace.
On success it frees the old modelist with fb_destroy_modelist(). Two
fields still point into that freed list.

One pointer is fb_display[i].mode, the mode a console is using.
fbcon_new_modelist() moves these pointers to the new list. It only does so
for consoles still mapped to the framebuffer. An unmapped console is
skipped and keeps its stale pointer. Unbinding fbcon, for example, sets
con2fb_map[i] to -1 but leaves fb_display[i].mode set. An
FBIOPUT_VSCREENINFO ioctl with FB_ACTIVATE_INV_MODE later reaches
fbcon_mode_deleted(). That function reads the stale fb_display[i].mode
through fb_mode_is_equal(). The read is a use-after-free.

The other pointer is fb_info->mode, the current mode. It is set through
the mode sysfs attribute. store_modes() does not update fb_info->mode, so
it is left pointing into the freed list. show_mode(), the attribute's read
handler, dereferences the stale fb_info->mode through mode_string(). The
read is a use-after-free.

Clear both pointers before freeing the list. Commit a1f305893074 ("fbcon:
Set fb_display[i]->mode to NULL when the mode is released") added the
helper fbcon_delete_modelist(). It clears every fb_display[i].mode that
points into a given list. So far it is called only from the unregister
path. Call it from store_modes() too, and set fb_info->mode to NULL.

## Which versions are affected by CVE-2026-63826?


## How do I fix CVE-2026-63826?

Apply the vendor's patch.

## Is CVE-2026-63826 being exploited?

There is no known exploitation of CVE-2026-63826 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-63826 and fix it if it is affected.

What it is: CVE-2026-63826 is an use after free vulnerability in Linux, published on 19 Jul 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-2026-63826 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-2026-63826/ (Markdown: https://insights.sbomify.com/CVE-2026-63826/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-63826
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-63826
- OSV: https://osv.dev/vulnerability/CVE-2026-63826

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-63826/
Summaries are generated and may contain mistakes; the official description above is the record.