# CVE-2026-98284: netlink: do not free nlk->groups while lockless readers can use it

> A use-after-free vulnerability in the Linux kernel netlink subsystem allows local attackers to cause denial of service or leak information via race conditions.

- **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:** 6 Oct 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-106371, BELL-CVE-2026-98284, DEBIAN-CVE-2026-98284, GHSA-x7q6-9x5c-r9x7, UBUNTU-CVE-2026-98284

## What is CVE-2026-98284?

CVE-2026-98284 is an use after free vulnerability in Linux, published on 6 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:

netlink: do not free nlk->groups while lockless readers can use it

netlink_realloc_groups() uses krealloc() under netlink_table_grab().
Whenever NLGRPSZ(groups) lands in a different kmalloc bucket, the old
bitmap is freed immediately.

Two readers of nlk->groups / nlk->ngroups do not hold the netlink
table lock:

1) sk_diag_dump_groups(). Hashed (bound) sockets are dumped from the
   rhashtable walk in __netlink_diag_dump(), which only holds RCU.
   Only the mc_list part of the dump takes nl_table_lock.

2) netlink_native_seq_show() (/proc/net/netlink), whose walk has been
   lockless since commit 21e4902aea80 ("netlink: Lockless lookup with
   RCU grace period in socket release").

Both can read a freed buffer, and sk_diag_dump_groups() can also read
past the end of the old (smaller) buffer if it happens to load the old
@groups pointer together with the new @ngroups value, copying the
result into a NETLINK_DIAG_GROUPS attribute.

This is the same class of bug that commit f773608026ee ("netlink:
access nlk groups safely in netlink bind and getname") fixed for bind()
and getname(); these two readers were missed. Simply grabbing the table
lock in sk_diag_dump_groups() is not an option, because it is also
called with nl_table_lock already held from the mc_list section of the
dump.

Make the lockless readers safe instead:

- Allocate a new bitmap and free the old one after an RCU grace period,
  instead of relying on the implicit kfree() done by krealloc().

- Publish @groups before @ngroups, both with release semantics, and have
  the lockless readers load @ngroups first. A reader can then never pair
  the new (bigger) size with the old (smaller) buffer, and a reader
  picking up the new pointer while still seeing the old size is
  guaranteed to see the initialized bitmap.

netlink_realloc_groups() is called from process context (bind() and
setsockopt()), so kfree_rcu_mightsleep() can be used, once the table
has been released.

## Which versions are affected by CVE-2026-98284?


## How do I fix CVE-2026-98284?

Apply the vendor's patch.

## Is CVE-2026-98284 being exploited?

There is no known exploitation of CVE-2026-98284 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98284 and fix it if it is affected.

What it is: CVE-2026-98284 is an use after free vulnerability in Linux, published on 6 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-2026-98284 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-2026-98284/ (Markdown: https://insights.sbomify.com/CVE-2026-98284/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98284
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98284
- OSV: https://osv.dev/vulnerability/CVE-2026-98284

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98284/
Summaries are generated and may contain mistakes; the official description above is the record.