---
id: CVE-2025-38591
title: 'bpf: Reject narrower access to pointer ctx fields'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  bpf: Reject narrower access to pointer ctx fields

  The following BPF program, simplified from a syzkaller repro, causes a
  kernel warning:

      r0 = *(u8 *)(r1 + 169);
   …
severity: medium
cvss: 5.5
cvssVector: 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H'
cvssSource: nvd
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= f96da09473b52c09125cc9bf7d7d4576ae8229e0 <
    7847c4140e06f6e87229faae22cc38525334c156
  - >-
    Linux >= f96da09473b52c09125cc9bf7d7d4576ae8229e0 <
    feae34c992eb7191862fb1594c704fbbf650fef8
  - >-
    Linux >= f96da09473b52c09125cc9bf7d7d4576ae8229e0 <
    33660d44e789edb4f303210c813fc56d56377a90
  - >-
    Linux >= f96da09473b52c09125cc9bf7d7d4576ae8229e0 <
    e2e9599f3503df7cf3569d2b6c50d5488fb59435
  - >-
    Linux >= f96da09473b52c09125cc9bf7d7d4576ae8229e0 <
    058a0da4f6d916a79b693384111bb80a90d73763
  - >-
    Linux >= f96da09473b52c09125cc9bf7d7d4576ae8229e0 <
    202900ceeef67458c964c2af6e1427c8e533ea7c
  - >-
    Linux >= f96da09473b52c09125cc9bf7d7d4576ae8229e0 <
    e09299225d5ba3916c91ef70565f7d2187e4cca0
  - Linux 4.13
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-06-10T20:41:20.077651Z'
published: '2025-08-19'
updated: '2026-09-14'
sourceUpdated: '2026-09-14T11:58:03.288Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2025-38591'
references:
  - url: 'https://git.kernel.org/stable/c/7847c4140e06f6e87229faae22cc38525334c156'
  - url: 'https://git.kernel.org/stable/c/feae34c992eb7191862fb1594c704fbbf650fef8'
  - url: 'https://git.kernel.org/stable/c/33660d44e789edb4f303210c813fc56d56377a90'
  - url: 'https://git.kernel.org/stable/c/e2e9599f3503df7cf3569d2b6c50d5488fb59435'
  - url: 'https://git.kernel.org/stable/c/058a0da4f6d916a79b693384111bb80a90d73763'
  - url: 'https://git.kernel.org/stable/c/202900ceeef67458c964c2af6e1427c8e533ea7c'
  - url: 'https://git.kernel.org/stable/c/e09299225d5ba3916c91ef70565f7d2187e4cca0'
  - url: 'https://cert-portal.siemens.com/productcert/html/ssa-019113.html'
    label: 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e
tags:
  - cve.org
  - nvd
epss: 0.00197
epssPercentile: 0.09777
patched:
  - linux_kernel 6.16.1
ingestedAt: '2026-09-08T15:33:26.997Z'
---

## Overview

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

bpf: Reject narrower access to pointer ctx fields

The following BPF program, simplified from a syzkaller repro, causes a
kernel warning:

    r0 = *(u8 *)(r1 + 169);
    exit;

With pointer field sk being at offset 168 in __sk_buff. This access is
detected as a narrower read in bpf_skb_is_valid_access because it
doesn't match offsetof(struct __sk_buff, sk). It is therefore allowed
and later proceeds to bpf_convert_ctx_access. Note that for the
"is_narrower_load" case in the convert_ctx_accesses(), the insn->off
is aligned, so the cnt may not be 0 because it matches the
offsetof(struct __sk_buff, sk) in the bpf_convert_ctx_access. However,
the target_size stays 0 and the verifier errors with a kernel warning:

    verifier bug: error during ctx access conversion(1)

This patch fixes that to return a proper "invalid bpf_context access
off=X size=Y" error on the load instruction.

The same issue affects multiple other fields in context structures that
allow narrow access. Some other non-affected fields (for sk_msg,
sk_lookup, and sockopt) were also changed to use bpf_ctx_range_ptr for
consistency.

Note this syzkaller crash was reported in the "Closes" link below, which
used to be about a different bug, fixed in
commit fce7bd8e385a ("bpf/verifier: Handle BPF_LOAD_ACQ instructions
in insn_def_regno()"). Because syzbot somehow confused the two bugs,
the new crash and repro didn't get reported to the mailing list.

## Affected

- `Linux >= f96da09473b52c09125cc9bf7d7d4576ae8229e0 < 7847c4140e06f6e87229faae22cc38525334c156`
- `Linux >= f96da09473b52c09125cc9bf7d7d4576ae8229e0 < feae34c992eb7191862fb1594c704fbbf650fef8`
- `Linux >= f96da09473b52c09125cc9bf7d7d4576ae8229e0 < 33660d44e789edb4f303210c813fc56d56377a90`
- `Linux >= f96da09473b52c09125cc9bf7d7d4576ae8229e0 < e2e9599f3503df7cf3569d2b6c50d5488fb59435`
- `Linux >= f96da09473b52c09125cc9bf7d7d4576ae8229e0 < 058a0da4f6d916a79b693384111bb80a90d73763`
- `Linux >= f96da09473b52c09125cc9bf7d7d4576ae8229e0 < 202900ceeef67458c964c2af6e1427c8e533ea7c`
- `Linux >= f96da09473b52c09125cc9bf7d7d4576ae8229e0 < e09299225d5ba3916c91ef70565f7d2187e4cca0`
- `Linux 4.13`

## Remediation

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