---
id: CVE-2026-99126
title: 's390/ctcm: Prevent XID null dereference'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  s390/ctcm: Prevent XID null dereference

  The mpc_validate_xid() function sets grp->saved_xid2->xid2_flag2 to 0x40
  to signal XID validation error. If peer XID is NULL or…
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 293d984f0e3604c04dcdbf00117ddc1e5d4b1909 <
    f9d9e2dadc9fbdfe01aeb6581978c3b59092919e
  - >-
    Linux >= 293d984f0e3604c04dcdbf00117ddc1e5d4b1909 <
    a7c3e1795e4fe5e6680cab7cd7eee0503b00a248
  - >-
    Linux >= 293d984f0e3604c04dcdbf00117ddc1e5d4b1909 <
    c11e435d334e4c311eaaf721e179a5ca6852c221
  - >-
    Linux >= 293d984f0e3604c04dcdbf00117ddc1e5d4b1909 <
    977dac6cc5531a8e058df05b6af94406b940cb9e
  - >-
    Linux >= 293d984f0e3604c04dcdbf00117ddc1e5d4b1909 <
    1525fb6e2f9f9a2c8c8723ee0959b1130a6b8213
  - >-
    Linux >= 293d984f0e3604c04dcdbf00117ddc1e5d4b1909 <
    34fa3607b7604b3052b19cec8b0ad644818cdd2a
  - >-
    Linux >= 293d984f0e3604c04dcdbf00117ddc1e5d4b1909 <
    8a2f7a4ad1d81612fa65bfa4d392ba1bb2f5eeab
  - >-
    Linux >= 293d984f0e3604c04dcdbf00117ddc1e5d4b1909 <
    b264d8422779d69febce914efc47a92a85cc382c
  - Linux 2.6.26
published: '2026-10-28'
updated: '2026-10-30'
sourceUpdated: '2026-10-30T12:41:59.971Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-99126'
references:
  - url: 'https://git.kernel.org/stable/c/f9d9e2dadc9fbdfe01aeb6581978c3b59092919e'
  - url: 'https://git.kernel.org/stable/c/a7c3e1795e4fe5e6680cab7cd7eee0503b00a248'
  - url: 'https://git.kernel.org/stable/c/c11e435d334e4c311eaaf721e179a5ca6852c221'
  - url: 'https://git.kernel.org/stable/c/977dac6cc5531a8e058df05b6af94406b940cb9e'
  - url: 'https://git.kernel.org/stable/c/1525fb6e2f9f9a2c8c8723ee0959b1130a6b8213'
  - url: 'https://git.kernel.org/stable/c/34fa3607b7604b3052b19cec8b0ad644818cdd2a'
  - url: 'https://git.kernel.org/stable/c/8a2f7a4ad1d81612fa65bfa4d392ba1bb2f5eeab'
  - url: 'https://git.kernel.org/stable/c/b264d8422779d69febce914efc47a92a85cc382c'
tags:
  - cve.org
epss: 0.00177
epssPercentile: 0.07329
ingestedAt: '2026-10-28T11:09:40.440Z'
---

## Overview

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

s390/ctcm: Prevent XID null dereference

The mpc_validate_xid() function sets grp->saved_xid2->xid2_flag2 to 0x40
to signal XID validation error. If peer XID is NULL or r/w channel
pairing mismatch happens, grp->saved_xid2 is never initialized. An
attempt to set the flag in such case leads to NULL dereference.

Fix this by using the always available priv->xid->xid2_flag2 instead of
grp->saved_xid2->xid2_flag2 for validation errors.

## Affected

- `Linux >= 293d984f0e3604c04dcdbf00117ddc1e5d4b1909 < f9d9e2dadc9fbdfe01aeb6581978c3b59092919e`
- `Linux >= 293d984f0e3604c04dcdbf00117ddc1e5d4b1909 < a7c3e1795e4fe5e6680cab7cd7eee0503b00a248`
- `Linux >= 293d984f0e3604c04dcdbf00117ddc1e5d4b1909 < c11e435d334e4c311eaaf721e179a5ca6852c221`
- `Linux >= 293d984f0e3604c04dcdbf00117ddc1e5d4b1909 < 977dac6cc5531a8e058df05b6af94406b940cb9e`
- `Linux >= 293d984f0e3604c04dcdbf00117ddc1e5d4b1909 < 1525fb6e2f9f9a2c8c8723ee0959b1130a6b8213`
- `Linux >= 293d984f0e3604c04dcdbf00117ddc1e5d4b1909 < 34fa3607b7604b3052b19cec8b0ad644818cdd2a`
- `Linux >= 293d984f0e3604c04dcdbf00117ddc1e5d4b1909 < 8a2f7a4ad1d81612fa65bfa4d392ba1bb2f5eeab`
- `Linux >= 293d984f0e3604c04dcdbf00117ddc1e5d4b1909 < b264d8422779d69febce914efc47a92a85cc382c`
- `Linux 2.6.26`

## Remediation

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