# CVE-2026-64576: nexthop: initialize extack in nh_res_bucket_migrate()

> An uninitialized pointer dereference in the Linux kernel nexthop module can cause a kernel panic, leading to denial of service.

- **Severity:** High 7.1 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/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:** 5 Aug 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-94461, BELL-CVE-2026-64576, DEBIAN-CVE-2026-64576, GHSA-pg7w-xrhc-whgh, UBUNTU-CVE-2026-64576

## What is CVE-2026-64576?

CVE-2026-64576 is a high-severity vulnerability in Linux, published on 5 Aug 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:

nexthop: initialize extack in nh_res_bucket_migrate()

nh_res_bucket_migrate() passes an uninitialized netlink_ext_ack to
call_nexthop_res_bucket_notifiers(). When
nh_notifier_res_bucket_info_init() fails (e.g. the kzalloc returns
-ENOMEM), the error is propagated back before any notifier sets
extack._msg, and the error path formats the stale pointer with
pr_err_ratelimited("%s\n", extack._msg). With CONFIG_INIT_STACK_NONE
this dereferences uninitialized stack memory:

  Oops: general protection fault, probably for non-canonical address ...
  KASAN: maybe wild-memory-access in range [...]
  RIP: 0010:string (lib/vsprintf.c:730)
   vsnprintf (lib/vsprintf.c:2945)
   _printk (kernel/printk/printk.c:2504)
   nh_res_bucket_migrate (net/ipv4/nexthop.c:1816)
   nh_res_table_upkeep (net/ipv4/nexthop.c:1866)
   rtm_new_nexthop (net/ipv4/nexthop.c:3323)
   rtnetlink_rcv_msg (net/core/rtnetlink.c:7076)
   netlink_sendmsg (net/netlink/af_netlink.c:1900)
  Kernel panic - not syncing: Fatal exception

Zero-initialize extack so _msg is NULL on error paths that never set it.

Weakness: CWE-457 (Use of Uninitialized Variable)

## Which versions are affected by CVE-2026-64576?


## How do I fix CVE-2026-64576?

Apply the vendor's patch.

## Is CVE-2026-64576 being exploited?

There is no known exploitation of CVE-2026-64576 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-64576 and fix it if it is affected.

What it is: CVE-2026-64576 is a high-severity vulnerability in Linux, published on 5 Aug 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-2026-64576 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-2026-64576/ (Markdown: https://insights.sbomify.com/CVE-2026-64576/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-64576
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-64576
- OSV: https://osv.dev/vulnerability/CVE-2026-64576

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-64576/
Summaries are generated and may contain mistakes; the official description above is the record.