---
id: CVE-2026-98040
title: |-
  In the Linux kernel, the following vulnerability has been resolved:

  bpf: Mark the zero register precise for a register-form NULL check

  check_cond_jmp_op() accepts "if rA <op> rB" as a NULL check for a
  nullable pointer rA when rB is a s…
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  bpf: Mark the zero register precise for a register-form NULL check

  check_cond_jmp_op() accepts "if rA <op> rB" as a NULL check for a
  nullable pointer rA when rB is a s…
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 2f4cb53eed448c1aeb6f4b40cf9c810716d8218c <
    ddca9a3b8833168dda3e62676648a636fb3f221c
  - >-
    Linux >= 2f4cb53eed448c1aeb6f4b40cf9c810716d8218c <
    6aed0134d3cda6382385a734ae0158eb7df6b142
  - Linux 7.1
published: '2026-09-25'
updated: '2026-09-25'
sourceUpdated: '2026-09-25T11:17:32.773'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-98040'
references:
  - url: 'https://git.kernel.org/stable/c/6aed0134d3cda6382385a734ae0158eb7df6b142'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/ddca9a3b8833168dda3e62676648a636fb3f221c'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
tags:
  - nvd
  - cve.org
ingestedAt: '2026-09-25T11:06:38.850Z'
---

## Overview

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

bpf: Mark the zero register precise for a register-form NULL check

check_cond_jmp_op() accepts "if rA <op> rB" as a NULL check for a
nullable pointer rA when rB is a scalar known to be zero,
lifts PTR_MAYBE_NULL from rA in the corresponding branch and does not
mark rB precise. Consider the following program:

  r0 = bpf_get_prandom_u32();
  r6 = 1;                  /* the r6 == 0 path is explored first */
  if (r0 == 0) goto 1f;
  r6 = 0;
1:
  r0 = bpf_map_lookup_elem(map, &0);  /* absent, NULL at runtime */
  if (r0 == r6) goto 2f;   /* taken as a NULL check for r0       */
  *(u8 *)(r0 + 0);         /* verifier: map value; runtime: zero */
2:
  return 0;

The r6 == 0 path is explored first and the dereference is accepted.
The r6 == 1 path is pruned at the checkpoint recorded for (1),
so the comparison is never verified with a non-zero r6. At runtime a
failed lookup returns NULL, NULL != 1 takes the non-NULL edge and the
program dereferences a pointer that is zero.

## Remediation

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