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

CVE-2026-98812 is fixed in 2 products on 1 platform, first by DEBIAN-CVE-2026-98812, released October 19, 2026. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2026-98812
- Priority: Routine
- CVSS: 4.7 (Moderate)
- EPSS: 0.0018
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Oct 18, 2026
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-98812

## 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.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 13.5 (trixie) | 6.12.113-1 | [DEBIAN-CVE-2026-98812](https://patchblox.com/security/data/fix/linux/debian-cve-2026-98812.md) | Oct 19, 2026 |
| Linux | linux Debian 14 | 7.2.10-1 | [DEBIAN-CVE-2026-98812](https://patchblox.com/security/data/fix/linux/debian-cve-2026-98812.md) | Oct 19, 2026 |
| Linux | linux-6.12 Debian 12.15 (bookworm) | 6.12.113-1~deb12u1 | [DEBIAN-CVE-2026-98812](https://patchblox.com/security/data/fix/linux/debian-cve-2026-98812.md) | Oct 19, 2026 |

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Data as of 2026-11-09T13:31:49Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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