# CVE-2025-38591

## Summary

- **CVE ID:** CVE-2025-38591
- **Severity:** MEDIUM
- **CVSS Score:** 5.5 (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H)
- **CWE:** N/A
- **Published:** Aug 19, 2025
- **Last Modified:** Sep 14, 2026

## Description

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 Products

- Linux — Linux (f96da09473b52c09125cc9bf7d7d4576ae8229e0)
- Linux — Linux (4.13)
- Linux — Linux (0)
- Linux — Linux (5.10.249)
- Linux — Linux (5.15.199)
- Linux — Linux (6.1.162)
- Linux — Linux (6.12.67)
- Linux — Linux (6.16.1)
- Linux — Linux (6.17)
- Linux — Linux (6.6.157)

## References

- [CNA](https://git.kernel.org/stable/c/7847c4140e06f6e87229faae22cc38525334c156)
- [CNA](https://git.kernel.org/stable/c/feae34c992eb7191862fb1594c704fbbf650fef8)
- [CNA](https://git.kernel.org/stable/c/33660d44e789edb4f303210c813fc56d56377a90)
- [CNA](https://git.kernel.org/stable/c/058a0da4f6d916a79b693384111bb80a90d73763)
- [CNA](https://git.kernel.org/stable/c/202900ceeef67458c964c2af6e1427c8e533ea7c)
- [CNA](https://git.kernel.org/stable/c/e09299225d5ba3916c91ef70565f7d2187e4cca0)
- [siemens-SADP](https://cert-portal.siemens.com/productcert/html/ssa-019113.html)
- [CNA](https://git.kernel.org/stable/c/e2e9599f3503df7cf3569d2b6c50d5488fb59435)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.20%
- **EPSS Percentile:** 9.7

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-18._