# CVE-2026-89948: batman-adv: bla: fix freeing of claims on meshif deletion

> A use-after-free vulnerability in the Linux kernel's batman-adv module allows attackers to cause a denial of service or potentially execute code during mesh interface deletion.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 16 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-101697, BELL-CVE-2026-89948, DEBIAN-CVE-2026-89948, GHSA-9m5r-cr5m-2hhr, UBUNTU-CVE-2026-89948

## What is CVE-2026-89948?

CVE-2026-89948 is an use after free vulnerability in Linux, published on 16 Sep 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:

batman-adv: bla: fix freeing of claims on meshif deletion

When the mesh interface is getting deleted, then
batadv_bla_del_backbone_claims() (via batadv_bla_purge_backbone_gw()) could
make sure that all claims gets removed. But this function is only executed
when bat_priv->bla.claim_hash is not NULL. And since batadv_bla_free() is
always setting it to NULL before it is (indirectly) called, it was never
actually executed.

But the batadv_bla_purge_claims() -> batadv_handle_unclaim() is at the
moment too fragile because the BLA code is not handling the rehashing in
batadv_bla_update_orig_address(). The stored backbone address doesn't have
to be the one actually used for the hash bucket selection during the
initial adding of the backbone. The batadv_handle_unclaim() can therefore
fail to find the respective backbone for the unclaim and then stop the
deletion.

But the actual backbone_gw object is not needed for the unclaim because all
relevant information is always provided by the caller. And the check for
the existence of the backbone_gw doesn't provide any additional security
check for the deletion of a claim.

## Which versions are affected by CVE-2026-89948?


## How do I fix CVE-2026-89948?

Apply the vendor's patch.

## Is CVE-2026-89948 being exploited?

There is no known exploitation of CVE-2026-89948 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89948 and fix it if it is affected.

What it is: CVE-2026-89948 is an use after free vulnerability in Linux, published on 16 Sep 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-2026-89948 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-2026-89948/ (Markdown: https://insights.sbomify.com/CVE-2026-89948/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89948
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89948
- OSV: https://osv.dev/vulnerability/CVE-2026-89948

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89948/
Summaries are generated and may contain mistakes; the official description above is the record.