---
id: CVE-2026-23398
title: 'icmp: fix NULL pointer dereference in icmp_tag_validation()'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  icmp: fix NULL pointer dereference in icmp_tag_validation()

  icmp_tag_validation() unconditionally dereferences the result of
  rcu_dereference(inet_protos[proto]) withou…
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 8ed1dc44d3e9e8387a104b1ae8f92e9a3fbf1b1e <
    571d9d7b650f02d1e38c01128817868bceac9edd
  - >-
    Linux >= 8ed1dc44d3e9e8387a104b1ae8f92e9a3fbf1b1e <
    d783fa413c702ff0f8f8bea63f862e28eeaf39e3
  - >-
    Linux >= 8ed1dc44d3e9e8387a104b1ae8f92e9a3fbf1b1e <
    1f9f2c6d4b2a613b7756fc5679c5116ba2ca0161
  - >-
    Linux >= 8ed1dc44d3e9e8387a104b1ae8f92e9a3fbf1b1e <
    b61529c357f1ee4d64836eb142a542d2e7ad67ce
  - >-
    Linux >= 8ed1dc44d3e9e8387a104b1ae8f92e9a3fbf1b1e <
    9647e99d2a617c355d2b378be0ff6d0e848fd579
  - >-
    Linux >= 8ed1dc44d3e9e8387a104b1ae8f92e9a3fbf1b1e <
    d938dd5a0ad780c891ea3bc94cae7405f11e618a
  - >-
    Linux >= 8ed1dc44d3e9e8387a104b1ae8f92e9a3fbf1b1e <
    1e4e2f5e48cec0cccaea9815fb9486c084ba41e2
  - >-
    Linux >= 8ed1dc44d3e9e8387a104b1ae8f92e9a3fbf1b1e <
    614aefe56af8e13331e50220c936fc0689cf5675
  - Linux 3.14
exploitAvailable: true
published: '2026-03-26'
updated: '2026-09-08'
sourceUpdated: '2026-09-08T08:45:59.359Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-23398'
references:
  - url: 'https://git.kernel.org/stable/c/571d9d7b650f02d1e38c01128817868bceac9edd'
  - url: 'https://git.kernel.org/stable/c/d783fa413c702ff0f8f8bea63f862e28eeaf39e3'
  - url: 'https://git.kernel.org/stable/c/1f9f2c6d4b2a613b7756fc5679c5116ba2ca0161'
  - url: 'https://git.kernel.org/stable/c/b61529c357f1ee4d64836eb142a542d2e7ad67ce'
  - url: 'https://git.kernel.org/stable/c/9647e99d2a617c355d2b378be0ff6d0e848fd579'
  - url: 'https://git.kernel.org/stable/c/d938dd5a0ad780c891ea3bc94cae7405f11e618a'
  - url: 'https://git.kernel.org/stable/c/1e4e2f5e48cec0cccaea9815fb9486c084ba41e2'
  - url: 'https://git.kernel.org/stable/c/614aefe56af8e13331e50220c936fc0689cf5675'
tags:
  - cve.org
  - exploit-available
epss: 0.00124
epssPercentile: 0.02503
exploits:
  github: 2
  githubRepos:
    - 'https://github.com/JohannesLks/CVE-2026-23398'
    - 'https://github.com/zpol/cve-2026-23398-poc'
  checkedAt: '2026-09-21T15:28:30.037Z'
ingestedAt: '2026-09-08T15:33:26.992Z'
---

## Overview

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

icmp: fix NULL pointer dereference in icmp_tag_validation()

icmp_tag_validation() unconditionally dereferences the result of
rcu_dereference(inet_protos[proto]) without checking for NULL.
The inet_protos[] array is sparse -- only about 15 of 256 protocol
numbers have registered handlers. When ip_no_pmtu_disc is set to 3
(hardened PMTU mode) and the kernel receives an ICMP Fragmentation
Needed error with a quoted inner IP header containing an unregistered
protocol number, the NULL dereference causes a kernel panic in
softirq context.

 Oops: general protection fault, probably for non-canonical address 0xdffffc0000000002: 0000 [#1] SMP KASAN NOPTI
 KASAN: null-ptr-deref in range [0x0000000000000010-0x0000000000000017]
 RIP: 0010:icmp_unreach (net/ipv4/icmp.c:1085 net/ipv4/icmp.c:1143)
 Call Trace:
  <IRQ>
  icmp_rcv (net/ipv4/icmp.c:1527)
  ip_protocol_deliver_rcu (net/ipv4/ip_input.c:207)
  ip_local_deliver_finish (net/ipv4/ip_input.c:242)
  ip_local_deliver (net/ipv4/ip_input.c:262)
  ip_rcv (net/ipv4/ip_input.c:573)
  __netif_receive_skb_one_core (net/core/dev.c:6164)
  process_backlog (net/core/dev.c:6628)
  handle_softirqs (kernel/softirq.c:561)
  </IRQ>

Add a NULL check before accessing icmp_strict_tag_validation. If the
protocol has no registered handler, return false since it cannot
perform strict tag validation.

## Affected

- `Linux >= 8ed1dc44d3e9e8387a104b1ae8f92e9a3fbf1b1e < 571d9d7b650f02d1e38c01128817868bceac9edd`
- `Linux >= 8ed1dc44d3e9e8387a104b1ae8f92e9a3fbf1b1e < d783fa413c702ff0f8f8bea63f862e28eeaf39e3`
- `Linux >= 8ed1dc44d3e9e8387a104b1ae8f92e9a3fbf1b1e < 1f9f2c6d4b2a613b7756fc5679c5116ba2ca0161`
- `Linux >= 8ed1dc44d3e9e8387a104b1ae8f92e9a3fbf1b1e < b61529c357f1ee4d64836eb142a542d2e7ad67ce`
- `Linux >= 8ed1dc44d3e9e8387a104b1ae8f92e9a3fbf1b1e < 9647e99d2a617c355d2b378be0ff6d0e848fd579`
- `Linux >= 8ed1dc44d3e9e8387a104b1ae8f92e9a3fbf1b1e < d938dd5a0ad780c891ea3bc94cae7405f11e618a`
- `Linux >= 8ed1dc44d3e9e8387a104b1ae8f92e9a3fbf1b1e < 1e4e2f5e48cec0cccaea9815fb9486c084ba41e2`
- `Linux >= 8ed1dc44d3e9e8387a104b1ae8f92e9a3fbf1b1e < 614aefe56af8e13331e50220c936fc0689cf5675`
- `Linux 3.14`

## Remediation

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