# CVE-2026-63949: auxdisplay: line-display: fix OOB read on zero-length message_store()

> A local attacker can trigger an out-of-bounds read in the Linux kernel auxdisplay driver by writing zero bytes to a sysfs attribute, potentially causing a crash or leaking memory.

- **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:** 19 Jul 2026
- **Also known as:** BELL-CVE-2026-63949, DEBIAN-CVE-2026-63949, GHSA-3qfr-7vgq-2884, UBUNTU-CVE-2026-63949

## What is CVE-2026-63949?

CVE-2026-63949 is a memory corruption 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:

auxdisplay: line-display: fix OOB read on zero-length message_store()

linedisp_display() unconditionally reads msg[count - 1] before
checking whether count is zero, so a write of zero bytes to the
message sysfs attribute hits msg[-1]:

	write(fd, "", 0);

	-> message_store(..., buf, count=0)
	   -> linedisp_display(linedisp, buf, count=0)
	      -> msg[count - 1] == '\n'  ; OOB read

The kernfs write buffer for that store is a 1-byte allocation
(kernfs_fop_write_iter() does kmalloc(len + 1) with len == 0),
so msg[-1] is a 1-byte read before the slab object. On a
KASAN-enabled kernel this trips an out-of-bounds report and
panics; on stock kernels it silently reads adjacent slab data
and, if that byte happens to be '\n', the following count--
wraps ssize_t 0 to -1 and is then passed to kmemdup_nul().

linedisp_display() is reached from the message_store() sysfs
callback (drivers/auxdisplay/line-display.c message attribute,
mode 0644) and from the in-tree initial-message setup with
count == -1, so the OOB path is only userspace-triggerable via
zero-byte writes; vfs_write() does not short-circuit on
count == 0 and kernfs_fop_write_iter() dispatches the store
callback regardless.

Guard the trailing-newline trim with a count check. The
existing if (!count) block then takes the clear-display path
unchanged.

Affects every auxdisplay driver that registers via
linedisp_register() / linedisp_attach(): ht16k33, max6959,
img-ascii-lcd, seg-led-gpio.

## Which versions are affected by CVE-2026-63949?


## How do I fix CVE-2026-63949?

Apply the vendor's patch.

## Is CVE-2026-63949 being exploited?

There is no known exploitation of CVE-2026-63949 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-63949 and fix it if it is affected.

What it is: CVE-2026-63949 is a memory corruption 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-2026-63949 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-2026-63949/ (Markdown: https://insights.sbomify.com/CVE-2026-63949/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-63949
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-63949
- OSV: https://osv.dev/vulnerability/CVE-2026-63949

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-63949/
Summaries are generated and may contain mistakes; the official description above is the record.