# CVE-2026-45886: bpf: Fix bpf_xdp_store_bytes proto for read-only arg

> Incorrect BPF helper prototype causes verifier rejection of valid read-only map accesses, potentially leading to denial of service.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 27 May 2026
- **Updated:** 27 May 2026
- **Also known as:** BELL-CVE-2026-45886, DEBIAN-CVE-2026-45886, GHSA-w77r-v3rv-5rcp, OESA-2026-2931, ROOT-OS-UBUNTU-2404-CVE-2026-45886, UBUNTU-CVE-2026-45886

## What is CVE-2026-45886?

CVE-2026-45886 is a medium-severity vulnerability in Linux kernel, published on 27 May 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

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.

Weakness: CWE-908 (Use of Uninitialized Resource)

## Which versions are affected by CVE-2026-45886?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-45886?

Apply the vendor's patch.

## Is CVE-2026-45886 being exploited?

There is no known exploitation of CVE-2026-45886 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-45886 and fix it if it is affected.

What it is: CVE-2026-45886 is a medium-severity vulnerability in Linux kernel, published on 27 May 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-45886 in the wild and no public exploit code.

Affected product: Linux kernel. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-45886/ (Markdown: https://insights.sbomify.com/CVE-2026-45886/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-45886
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-45886
- OSV: https://osv.dev/vulnerability/CVE-2026-45886

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-45886/
Summaries are generated and may contain mistakes; the official description above is the record.