---
id: CVE-2026-97420
title: |-
  In the Linux kernel, the following vulnerability has been resolved:

  bpf: NUL-terminate replaced sysctl value

  When writing to sysctls, proc_sys_call_handler() guarantees that the
  buffer passed to proc handlers is NUL-terminated
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  bpf: NUL-terminate replaced sysctl value

  When writing to sysctls, proc_sys_call_handler() guarantees that the
  buffer passed to proc handlers is NUL-terminated. If
  bpf_…
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <
    76c14b10f50eb0afcc76e244562fa2d8c661e224
  - >-
    Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <
    3b2814dd842a565fcf9cc370156e1ba9eae16239
  - >-
    Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <
    a66e3b5bacf38d6ab29fa05a9754f7a114485605
  - Linux < 6.12.111
  - Linux < 6.18.53
  - Linux (all versions)
published: '2026-09-24'
updated: '2026-09-25'
sourceUpdated: '2026-09-25T13:17:25.540'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-97420'
references:
  - url: 'https://git.kernel.org/stable/c/3b2814dd842a565fcf9cc370156e1ba9eae16239'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/76c14b10f50eb0afcc76e244562fa2d8c661e224'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/a66e3b5bacf38d6ab29fa05a9754f7a114485605'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
tags:
  - nvd
  - cve.org
ingestedAt: '2026-09-24T16:47:15.884Z'
---

## Overview

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

bpf: NUL-terminate replaced sysctl value

When writing to sysctls, proc_sys_call_handler() guarantees that the
buffer passed to proc handlers is NUL-terminated. If
bpf_sysctl_set_new_value() replaces the pending sysctl value, it can
hand a replacement buffer directly to proc handlers. However, the
helper currently copies only buf_len bytes into that buffer without
appending a NUL terminator, leaving downstream parsers vulnerable to
out-of-bounds access.

Fix this by appending a '\0' after the replaced value to restore the
expected sysctl semantics. Since the helper already rejects buf_len
greater than PAGE_SIZE - 1, there is always room for the extra byte.

Reproduced in a QEMU x86_64 guest booted with KASAN while exercising
the sysctl replacement path with a cgroup/sysctl BPF program. The
reproducer targets `/proc/sys/net/core/flow_limit_cpu_bitmap`, fills
the original user write buffer with non-zero bytes, and overrides the
sysctl value so the replacement buffer lacks a terminating NUL. Under
that setup, the pre-fix kernel reported:

  BUG: KASAN: slab-out-of-bounds in strnchrnul+0x72/0x90
  Read of size 1 at addr ffff88800de57000 by task repro_patch3/66
  CPU: 0 UID: 0 PID: 66 Comm: repro_patch3 Not tainted 7.1.0-rc3-00269-g8370ca1f87cc #6 PREEMPT(lazy)
  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
  Call Trace:
   <TASK>
   dump_stack_lvl+0x68/0xa0
   print_report+0xcb/0x5e0
   ? __virt_addr_valid+0x21d/0x3f0
   ? strnchrnul+0x72/0x90
   ? strnchrnul+0x72/0x90
   kasan_report+0xca/0x100
   ? strnchrnul+0x72/0x90
   strnchrnul+0x72/0x90
   bitmap_parse+0x37/0x2e0
   flow_limit_cpu_sysctl+0xc6/0x840
   ? __pfx_flow_limit_cpu_sysctl+0x10/0x10
   ? __kvmalloc_node_noprof+0x5ba/0x870
   proc_sys_call_handler+0x31d/0x480
   ? __pfx_proc_sys_call_handler+0x10/0x10
   ? selinux_file_permission+0x39f/0x500
   ? lock_is_held_type+0x9e/0x120
   vfs_write+0x98e/0x1000
   ...
   </TASK>
  The buggy address is located 0 bytes to the right of
  allocated 4096-byte region [ffff88800de56000, ffff88800de57000)
With this fix applied, rerunning the same sysctl-targeted path yields
no corresponding KASAN reports.

## Remediation

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