# CVE-2026-63876: serial: zs: Convert to use a platform device

> A null pointer dereference in the Linux kernel Z85C30 serial driver causes a system crash during initialization, leading to 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:** 19 Jul 2026
- **Updated:** 19 Jul 2026
- **Also known as:** BELL-CVE-2026-63876, DEBIAN-CVE-2026-63876, GHSA-hqmx-j5v3-63h6, UBUNTU-CVE-2026-63876

## What is CVE-2026-63876?

CVE-2026-63876 is a 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:

serial: zs: Convert to use a platform device

Prevent a crash from happening as the first serial port is initialised:

  Console: switching to mono frame buffer device 160x64
  fb0: PMAG-AA frame buffer device at tc0
  DECstation Z85C30 serial driver version 0.10
  CPU 0 Unable to handle kernel paging request at virtual address 0000002c, epc == 803ab00c, ra == 803aafe0
  Oops[#1]:
  CPU: 0 PID: 1 Comm: swapper Not tainted 6.4.0-rc3-00031-g84a9582fd203-dirty #57
  $ 0   : 00000000 10012c00 803aaeb0 00000000
  $ 4   : 80e12f60 80e12f50 80e12f58 81000030
  $ 8   : 00000000 805ff37c 00000000 33433538
  $12   : 65732030 00000006 80c2915d 6c616972
  $16   : 80e12f00 807b7630 00000000 00000000
  $20   : 00000004 00000348 000001a0 807623b8
  $24   : 00000018 00000000
  $28   : 80c24000 80c25d60 8078b148 803aafe0
  Hi    : 00000000
  Lo    : 00000000
  epc   : 803ab00c serial_base_ctrl_add+0x78/0xf4
  ra    : 803aafe0 serial_base_ctrl_add+0x4c/0xf4
  Status: 10012c03	KERNEL EXL IE
  Cause : 00000008 (ExcCode 02)
  BadVA : 0000002c
  PrId  : 00000440 (R4400SC)
  Modules linked in:
  Process swapper (pid: 1, threadinfo=(ptrval), task=(ptrval), tls=00000000)
  Stack : 80760000 00000cc0 00400044 00400040 803aa02c 80d61ab8 00000000 807b7630
          80760000 807623b8 807b7628 803aa644 80386998 00000000 80e17780 80220f68
          80e17780 80d61ab8 80c17d80 80e17780 80e17780 8063c798 80e17780 80383fa0
          00000010 80e17780 00000000 80386998 807a0000 00000000 00400040 8038f848
          807623b8 80d61ab8 00000004 80e17780 00000000 803a68e4 80c25e2c 803bb884
          ...
  Call Trace:
  [<803ab00c>] serial_base_ctrl_add+0x78/0xf4
  [<803aa644>] serial_core_register_port+0x174/0x69c
  [<8077e9ac>] zs_init+0xc8/0xfc
  [<800404d4>] do_one_initcall+0x40/0x2ac
  [<8076cecc>] kernel_init_freeable+0x1e4/0x270
  [<80605bec>] kernel_init+0x20/0x108
  [<800431e8>] ret_from_kernel_thread+0x14/0x1c

  Code: 2442aeb0  ae120024  ae0200d0 <8c67002c> 50e00001  8c670000  3c06806e  3c05806e  afb30010

  ---[ end trace 0000000000000000 ]---

(report at the offending commit) -- where a pointer is dereferenced that
has been derived from a null pointer to the port's parent device.

Since no device is available with legacy probing and it's not anymore a
preferable way to discover devices anyway, switch the driver to using a
platform device and use it as the port's parent device.  Update resource
handling accordingly and only request the actual span of addresses used
within the slot, which will have had its resource already requested by
generic platform device code.

Use platform_driver_probe() not just because SCC devices are fixed with
solder on board and not straightforward to remove, but foremost because
the associated TTY's major device number is the same as used by the dz
driver and the first driver to claim it will prevent the other one from
using it.  Either one DZ device or some SCC devices will be present in a
given system but never both at a time, and therefore we want the major
device number to be claimed by the first driver to actually successfully
bind to its device and platform_driver_probe() is a way to fulfil that.

An unfortunate consequence of the switch to a platform device is we now
hand the console over from the bootconsole much later in the bootstrap.
The firmware console handler appears good enough though to work so late
and in particular with interrupts enabled.

Since there is one way only remaining to reach zs_reset() now, remove
the port initialisation marker as no longer needed and go through the
channel reset unconditionally.

## Which versions are affected by CVE-2026-63876?


## How do I fix CVE-2026-63876?

Apply the vendor's patch.

## Is CVE-2026-63876 being exploited?

There is no known exploitation of CVE-2026-63876 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-63876 and fix it if it is affected.

What it is: CVE-2026-63876 is a 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-2026-63876 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-2026-63876/ (Markdown: https://insights.sbomify.com/CVE-2026-63876/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-63876
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-63876
- OSV: https://osv.dev/vulnerability/CVE-2026-63876

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-63876/
Summaries are generated and may contain mistakes; the official description above is the record.