# CVE-2026-89702: nfsd: size fh_verify server sockaddr slot by xpt_locallen

> A buffer overflow in Linux kernel NFS tracepoints allows attackers to leak memory or cause denial of service via crafted UDP requests.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 11 Sep 2026
- **Updated:** 21 Oct 2026
- **Also known as:** AZL-100449, BELL-CVE-2026-89702, DEBIAN-CVE-2026-89702, GHSA-vwc6-74mr-xh83, UBUNTU-CVE-2026-89702

## What is CVE-2026-89702?

CVE-2026-89702 is a critical memory corruption vulnerability in Linux, published on 11 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

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

nfsd: size fh_verify server sockaddr slot by xpt_locallen

The nfsd_fh_verify and nfsd_fh_verify_err tracepoints declare the
server sockaddr slot sized by xpt_remotelen but fill it from
xpt_local using xpt_locallen:

    TP_STRUCT__entry(
            ...
            __sockaddr(server, rqstp->rq_xprt->xpt_remotelen)
            ...
    )
    TP_fast_assign(
            ...
            __assign_sockaddr(server, &rqstp->rq_xprt->xpt_local,
                              rqstp->rq_xprt->xpt_locallen);
            ...
    )

When xpt_locallen exceeds xpt_remotelen, __assign_sockaddr's memcpy
writes past the reserved ring-buffer slot. In the reverse direction
(xpt_locallen < xpt_remotelen) the slot is oversized and the
unwritten tail leaks prior ring-buffer contents to trace consumers.

The write-past-end case is reachable on NFS/UDP. svc_xprt_set_remote()
is only called from svc_tcp_accept() (net/sunrpc/svcsock.c) and from
the RDMA connect path; svc_create_socket() for UDP calls only
svc_xprt_set_local(), so xpt_remotelen stays 0 for the xprt's
lifetime. Every fh_verify trace for an NFSv2/v3-over-UDP request
then copies 16 or 28 bytes from xpt_local into a zero-byte slot.

The other NFSD tracepoints that record the server address
(NFSD_TRACE_PROC_CALL_FIELDS, NFSD_TRACE_PROC_RES_FIELDS,
SVC_RQST_ENDPOINT_FIELDS) already size the server slot by
xpt_locallen; nfsd_fh_verify and nfsd_fh_verify_err were the only
exceptions.

Fix by sizing the server slot with xpt_locallen so the declared slot
matches the copy length. The client slot and its assignment already
agree on xpt_remotelen and are left untouched.

## Which versions are affected by CVE-2026-89702?


## How do I fix CVE-2026-89702?

Apply the vendor's patch.

## Is CVE-2026-89702 being exploited?

There is no known exploitation of CVE-2026-89702 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89702 and fix it if it is affected.

What it is: CVE-2026-89702 is a critical memory corruption vulnerability in Linux, published on 11 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-89702 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-2026-89702/ (Markdown: https://insights.sbomify.com/CVE-2026-89702/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89702
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89702
- OSV: https://osv.dev/vulnerability/CVE-2026-89702

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89702/
Summaries are generated and may contain mistakes; the official description above is the record.