# CVE-2026-98812: net/mctp: publish the mctp_dev only after it is initialised

> A race condition in the Linux kernel MCTP subsystem allows local attackers to trigger a null pointer dereference and system crash.

- **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:** 18 Oct 2026
- **Updated:** 21 Oct 2026
- **Also known as:** AZL-109286, BELL-CVE-2026-98812, DEBIAN-CVE-2026-98812, GHSA-737h-gm8x-wcgc, UBUNTU-CVE-2026-98812

## What is CVE-2026-98812?

CVE-2026-98812 is a vulnerability in Linux, published on 18 Oct 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:

net/mctp: publish the mctp_dev only after it is initialised

mctp_add_dev() links the new mctp_dev into dev->mctp_ptr before mdev->dev
is assigned, so a reader that picks the device up in that window
dereferences a net_device pointer that is still NULL:

KASAN: null-ptr-deref in range [0x00000000000000b0-0x00000000000000b7]
Call Trace:
 <TASK>
 ? __pfx_mctp_sendmsg (./include/linux/sockptr.h:49)
 ? __pfx_mctp_dst_output (net/mctp/route.c:41)
 ? selinux_socket_sendmsg (security/selinux/hooks.c:5278)
 ____sys_sendmsg (net/socket.c:775 (discriminator 1) net/socket.c:790
 (discriminator 1) net/socket.c:2684 (discriminator 1))
 ? __pfx_____sys_sendmsg (net/socket.c:1131)
 ? __pfx_copy_msghdr_from_user (net/socket.c:2590)
 ? update_cfs_rq_load_avg (kernel/sched/fair.c:5478)
 ___sys_sendmsg (net/socket.c:2738)
 ? __pfx____sys_sendmsg (net/socket.c:2625)
 ? perf_event_task_tick (./include/linux/rcupdate.h:838)
 ? sched_tick (kernel/sched/core.c:5818)
 ? clockevents_program_event (kernel/time/clockevents.c:372)
 ? fdget (./include/linux/rcupdate.h:873 fs/file.c:1100)
 __sys_sendmsg (net/socket.c:2770)
 ? __pfx___sys_sendmsg (net/socket.c:2751)
 do_syscall_64 (arch/x86/entry/syscall_64.c:63)
 entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:121)
 </TASK>

Fix by publishing only once the object is fully initialised:
__mctp_dev_get() runs under rcu_read_lock() only and hands
this object to readers as soon as mctp_ptr is assigned, so
they must never observe mdev->dev == NULL.

## Which versions are affected by CVE-2026-98812?


## How do I fix CVE-2026-98812?

Apply the vendor's patch.

## Is CVE-2026-98812 being exploited?

There is no known exploitation of CVE-2026-98812 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98812 and fix it if it is affected.

What it is: CVE-2026-98812 is a vulnerability in Linux, published on 18 Oct 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-2026-98812 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-2026-98812/ (Markdown: https://insights.sbomify.com/CVE-2026-98812/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98812
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98812
- OSV: https://osv.dev/vulnerability/CVE-2026-98812

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98812/
Summaries are generated and may contain mistakes; the official description above is the record.