# CVE-2026-98643: bpf: Fix out-of-bounds read of rtt_min in sock_ops

> A local attacker with BPF privileges can read out-of-bounds kernel memory via sock_ops, potentially leaking sensitive kernel pointers.

- **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-109140, BELL-CVE-2026-98643, DEBIAN-CVE-2026-98643, GHSA-xg7q-jpqp-fc7g, UBUNTU-CVE-2026-98643

## What is CVE-2026-98643?

CVE-2026-98643 is a 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 out-of-bounds read of rtt_min in sock_ops

A sockops prog reading skops->rtt_min never checks the sk type: on the
tcp_conn_request() path sock_ops->sk is a request_sock (non-full), and the
ctx rewrite casts it to a tcp_sock (full) and reads rtt_min past the end of
the request_sock, returning dirty adjacent memory.

	SEC("sockops")
	int prog(struct bpf_sock_ops *skops)
	{
		switch (skops->op) {
		case BPF_SOCK_OPS_RWND_INIT:
			leak = skops->rtt_min;   /* reads the request_sock OOB */
		...
		}
	}

For instance one such read returned rtt_min=0xffff8881, the high half of a
leaked kernel pointer.

Guarding that cast is exactly what SOCK_OPS_GET_FIELD() does -- it checks
is_locked_tcp_sock and returns 0 when sock_ops->sk is not a locked full
socket. Every other tcp_sock field in sock_ops goes through it; rtt_min is
the only one open-coded, so it skips the check.

Read rtt_min through SOCK_OPS_GET_FIELD() too. rtt_min is a bit special:
it is a struct minmax and we only want the current min, so pass
rtt_min.s[0].v. That is equivalent to the old hand-computed offset

	offsetof(struct tcp_sock, rtt_min) + sizeof_field(struct minmax_sample, t)

(s[0] sits at rtt_min + 0 and .v at + sizeof(.t), i.e. what minmax_get()
returns), so the loaded field is unchanged and only the full-sock guard is
added. The two BUILD_BUG_ON()s that protected the hand-computed offset
are no longer needed.

Before patch:

	0: r1 = *(u64 *)(r1 +0)      ; r1 = skops->sk
	1: r1 = *(u32 *)(r1 +2324)   ; ((tcp_sock *)sk)->rtt_min.s[0].v

After patch:

	0: *(u64 *)(r1 +56) = r9
	1: r9 = *(u8 *)(r1 +50)      ; is_locked_tcp_sock
	2: if r9 == 0 goto pc+4      ; not a locked full sock -> 0
	3: r9 = *(u64 *)(r1 +56)
	4: r1 = *(u64 *)(r1 +0)      ; r1 = skops->sk
	5: r1 = *(u32 *)(r1 +2324)   ; rtt_min.s[0].v
	6: goto pc+2
	7: r9 = *(u64 *)(r1 +56)
	8: r1 = 0

## Which versions are affected by CVE-2026-98643?


## How do I fix CVE-2026-98643?

Apply the vendor's patch.

## Is CVE-2026-98643 being exploited?

There is no known exploitation of CVE-2026-98643 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98643 and fix it if it is affected.

What it is: CVE-2026-98643 is a 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-2026-98643 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-2026-98643/ (Markdown: https://insights.sbomify.com/CVE-2026-98643/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98643
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98643
- OSV: https://osv.dev/vulnerability/CVE-2026-98643

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98643/
Summaries are generated and may contain mistakes; the official description above is the record.