---
id: CVE-2026-98525
title: 'mctp: route: iterate socket tag list in mctp_lookup_prealloc_tag()'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  mctp: route: iterate socket tag list in mctp_lookup_prealloc_tag()

  When a socket transmits a packet with MCTP_TAG_PREALLOC set,
  mctp_lookup_prealloc_tag() iterates ove…
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 63ed1aab3d40aa61aaa66819bdce9377ac7f40fa <
    09299addab11857e92eca55cd8ef3350b927c90c
  - >-
    Linux >= 63ed1aab3d40aa61aaa66819bdce9377ac7f40fa <
    e35cb500dd14882f8dee61783fccd1823fd3ab0d
  - >-
    Linux >= 63ed1aab3d40aa61aaa66819bdce9377ac7f40fa <
    f178300e2f56ca9ec2a3a0090608730bbee0af7b
  - >-
    Linux >= 63ed1aab3d40aa61aaa66819bdce9377ac7f40fa <
    26cc0e69cce062cd3aa6fae33074684669c35a71
  - Linux 5.18
published: '2026-10-18'
updated: '2026-10-18'
sourceUpdated: '2026-10-18T15:17:43.216Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-98525'
references:
  - url: 'https://git.kernel.org/stable/c/09299addab11857e92eca55cd8ef3350b927c90c'
  - url: 'https://git.kernel.org/stable/c/e35cb500dd14882f8dee61783fccd1823fd3ab0d'
  - url: 'https://git.kernel.org/stable/c/f178300e2f56ca9ec2a3a0090608730bbee0af7b'
  - url: 'https://git.kernel.org/stable/c/26cc0e69cce062cd3aa6fae33074684669c35a71'
tags:
  - cve.org
ingestedAt: '2026-10-18T15:45:12.281Z'
---

## Overview

In the Linux kernel, the following vulnerability has been resolved:

mctp: route: iterate socket tag list in mctp_lookup_prealloc_tag()

When a socket transmits a packet with MCTP_TAG_PREALLOC set,
mctp_lookup_prealloc_tag() iterates over the per-netns &mns->keys list
and matches netid, req_tag, peer_addr, and manual_alloc, without
checking whether tmp->sk == &msk->sk. This allows any MCTP socket in the
same network namespace to use and consume another socket's preallocated
tag.

Iterate the socket's own tag list (&msk->keys via sklist) instead of the
namespace-wide &mns->keys list in mctp_lookup_prealloc_tag(), ensuring
that only tags allocated by msk are matched.

Tested in QEMU against Linux 7.3.0-rc3 by allocating a manual tag
(0x18) on socket A via SIOCMCTPALLOCTAG for peer EID 9 and sending a
4-byte message with MCTP_TAG_PREALLOC from socket B in the same network
namespace. On the unfixed kernel, sendto(sock_b) using socket A's
preallocated tag succeeds (ret = 4); with this patch applied,
sendto(sock_b) fails with -ENOENT (errno = 2) while sendto(sock_a)
succeeds (ret = 4).

## Affected

- `Linux >= 63ed1aab3d40aa61aaa66819bdce9377ac7f40fa < 09299addab11857e92eca55cd8ef3350b927c90c`
- `Linux >= 63ed1aab3d40aa61aaa66819bdce9377ac7f40fa < e35cb500dd14882f8dee61783fccd1823fd3ab0d`
- `Linux >= 63ed1aab3d40aa61aaa66819bdce9377ac7f40fa < f178300e2f56ca9ec2a3a0090608730bbee0af7b`
- `Linux >= 63ed1aab3d40aa61aaa66819bdce9377ac7f40fa < 26cc0e69cce062cd3aa6fae33074684669c35a71`
- `Linux 5.18`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.