# CVE-2026-98647: bpf: Fix divide-by-zero in btf_struct_walk()

> A local attacker with low privileges can cause a kernel crash via divide-by-zero in BPF struct walking when loading specific programs.

- **Severity:** Not scored
- **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:** 18 Oct 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-109206, BELL-CVE-2026-98647, DEBIAN-CVE-2026-98647, GHSA-p98x-gg62-cxq2, UBUNTU-CVE-2026-98647

## What is CVE-2026-98647?

CVE-2026-98647 is a denial of service vulnerability in Linux, published on 18 Oct 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 divide-by-zero in btf_struct_walk()

When an access goes past the struct and the last member is a flexible
array, btf_struct_walk() folds the offset back into a single element with
(off - moff) % t->size, but never checks that the element type has a size.

BTF takes an empty struct, so this in program BTF

	/* event could be empty */
	struct event {
 #ifdef HAVE_TIMESTAMP
		__u64 ts;
 #endif
	};

	struct batch {
		int nr;
		struct event events[];
	};

divides by zero at prog load time. Getting there needs a PTR_TO_BTF_ID that
is not MEM_ALLOC, e.g. a plain read of a local kptr stashed in a map from a
sleepable program.

Oops: divide error: 0000 [#1] SMP KASAN PTI
RIP: 0010:btf_struct_walk+0x53f/0x1570
Call Trace:
 <TASK>
 btf_struct_access+0x42a/0xcd0
 check_ptr_to_btf_access+0x4dc/0x1160
 check_mem_access+0x3a45/0x8740
 check_load_mem+0x36a/0xd10
 do_check_common+0x3ef0/0xb210
 bpf_check+0x6d3b/0x8580
 bpf_prog_load+0xf7c/0x2720
 __sys_bpf+0xa83/0x3690
 __x64_sys_bpf+0xc7/0x150
 x64_sys_call+0x1f3f/0x27e0
 do_syscall_64+0xe5/0x610
 entry_SYSCALL_64_after_hwframe+0x76/0x7e
 </TASK>

Reject a zero-sized element type. The fixed array path in the same function
already bails out on the same thing:

	btf_struct_walk()
	...
		/* skip empty array */
		if (moff == mtrue_end)
			continue;

		msize /= total_nelems;

## Which versions are affected by CVE-2026-98647?


## How do I fix CVE-2026-98647?

Apply the vendor's patch.

## Is CVE-2026-98647 being exploited?

There is no known exploitation of CVE-2026-98647 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98647 and fix it if it is affected.

What it is: CVE-2026-98647 is a denial of service vulnerability in Linux, published on 18 Oct 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-2026-98647 in the wild and no public exploit code.

Affected product: Linux. 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-2026-98647/ (Markdown: https://insights.sbomify.com/CVE-2026-98647/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98647
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98647
- OSV: https://osv.dev/vulnerability/CVE-2026-98647

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98647/
Summaries are generated and may contain mistakes; the official description above is the record.