---
id: CVE-2026-45886
title: 'bpf: Fix bpf_xdp_store_bytes proto for read-only arg'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  bpf: Fix bpf_xdp_store_bytes proto for read-only arg

  While making some maps in Cilium read-only from the BPF side, we noticed
  that the bpf_xdp_store_bytes proto is inc…
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 3f364222d032eea6b245780e845ad213dab28cdd <
    ffb5d1c5e3933b947fc7303ad68bf0c536d0c85e
  - >-
    Linux >= 3f364222d032eea6b245780e845ad213dab28cdd <
    ddc34a1b85505c919026ddc82fafdada9a160b15
  - >-
    Linux >= 3f364222d032eea6b245780e845ad213dab28cdd <
    0db169a91381a473b7974021d1c02f8da72c5775
  - >-
    Linux >= 3f364222d032eea6b245780e845ad213dab28cdd <
    d7b87adeb0eb539b9b824b101bb14fb01e41240b
  - >-
    Linux >= 3f364222d032eea6b245780e845ad213dab28cdd <
    57f7f6a0ad04a65c8a7a067b2f56cbbf2aec9e52
  - >-
    Linux >= 3f364222d032eea6b245780e845ad213dab28cdd <
    6557f1565d779851c4db9c488c49c05a47a6e72f
  - Linux 5.18
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-11-06T15:43:32.501489Z'
published: '2026-05-27'
updated: '2026-11-06'
sourceUpdated: '2026-11-06T15:53:10.803Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-45886'
references:
  - url: 'https://git.kernel.org/stable/c/ffb5d1c5e3933b947fc7303ad68bf0c536d0c85e'
  - url: 'https://git.kernel.org/stable/c/ddc34a1b85505c919026ddc82fafdada9a160b15'
  - url: 'https://git.kernel.org/stable/c/0db169a91381a473b7974021d1c02f8da72c5775'
  - url: 'https://git.kernel.org/stable/c/d7b87adeb0eb539b9b824b101bb14fb01e41240b'
  - url: 'https://git.kernel.org/stable/c/57f7f6a0ad04a65c8a7a067b2f56cbbf2aec9e52'
  - url: 'https://git.kernel.org/stable/c/6557f1565d779851c4db9c488c49c05a47a6e72f'
tags:
  - cve.org
epss: 0.0016
epssPercentile: 0.0526
ingestedAt: '2026-11-06T16:57:43.392Z'
---

## Overview

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

bpf: Fix bpf_xdp_store_bytes proto for read-only arg

While making some maps in Cilium read-only from the BPF side, we noticed
that the bpf_xdp_store_bytes proto is incorrect. In particular, the
verifier was throwing the following error:

  ; ret = ctx_store_bytes(ctx, l3_off + offsetof(struct iphdr, saddr),
                          &nat->address, 4, 0);
  635: (79) r1 = *(u64 *)(r10 -144)     ; R1=ctx() R10=fp0 fp-144=ctx()
  636: (b4) w2 = 26                     ; R2=26
  637: (b4) w4 = 4                      ; R4=4
  638: (b4) w5 = 0                      ; R5=0
  639: (85) call bpf_xdp_store_bytes#190
  write into map forbidden, value_size=6 off=0 size=4

nat comes from a BPF_F_RDONLY_PROG map, so R3 is a PTR_TO_MAP_VALUE.
The verifier checks the helper's memory access to R3 in
check_mem_size_reg, as it reaches ARG_CONST_SIZE argument. The third
argument has expected type ARG_PTR_TO_UNINIT_MEM, which includes the
MEM_WRITE flag. The verifier thus checks for a BPF_WRITE access on R3.
Given R3 points to a read-only map, the check fails.

Conversely, ARG_PTR_TO_UNINIT_MEM can also lead to the helper reading
from uninitialized memory.

This patch simply fixes the expected argument type to match that of
bpf_skb_store_bytes.

## Affected

- `Linux >= 3f364222d032eea6b245780e845ad213dab28cdd < ffb5d1c5e3933b947fc7303ad68bf0c536d0c85e`
- `Linux >= 3f364222d032eea6b245780e845ad213dab28cdd < ddc34a1b85505c919026ddc82fafdada9a160b15`
- `Linux >= 3f364222d032eea6b245780e845ad213dab28cdd < 0db169a91381a473b7974021d1c02f8da72c5775`
- `Linux >= 3f364222d032eea6b245780e845ad213dab28cdd < d7b87adeb0eb539b9b824b101bb14fb01e41240b`
- `Linux >= 3f364222d032eea6b245780e845ad213dab28cdd < 57f7f6a0ad04a65c8a7a067b2f56cbbf2aec9e52`
- `Linux >= 3f364222d032eea6b245780e845ad213dab28cdd < 6557f1565d779851c4db9c488c49c05a47a6e72f`
- `Linux 5.18`

## Remediation

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