# CVE-2026-63834: batman-adv: tp_meter: restrict number of unacked list entries

> An attacker can cause a denial of service in the Linux kernel's batman-adv module by exhausting memory or CPU resources via crafted network packets.

- **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:** 19 Jul 2026
- **Updated:** 17 Aug 2026
- **Also known as:** BELL-CVE-2026-63834, DEBIAN-CVE-2026-63834, GHSA-946h-284m-vvp5, ROOT-OS-DEBIAN-11-CVE-2026-63834, ROOT-OS-UBUNTU-2204-CVE-2026-63834, UBUNTU-CVE-2026-63834

## What is CVE-2026-63834?

CVE-2026-63834 is a denial of service vulnerability in Linux, published on 19 Jul 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: tp_meter: restrict number of unacked list entries

When the unacked_list is unbound, an attacker could send messages with
small lengths and appropriated seqno + gaps to force the receiver to
allocate more and more unacked_list entries. And the end either causing an
out-of-memory situation or increase the management overhead for the (large)
list that significant portions of CPU cycles are wasted in searching
through the list.

When limiting the list to a specific number, it is important to still
correctly add a new entry to the list. But if the list became larger than
the limit, the last entry of the list (with the highest seqno) must be
dropped to still allow the earlier seqnos to finish and therefore to
continue the process. Otherwise, the process might get stuck with too high
seqnos which are not handled by batadv_tp_ack_unordered().

## Which versions are affected by CVE-2026-63834?


## How do I fix CVE-2026-63834?

Apply the vendor's patch.

## Is CVE-2026-63834 being exploited?

There is no known exploitation of CVE-2026-63834 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-63834 and fix it if it is affected.

What it is: CVE-2026-63834 is a denial of service vulnerability in Linux, published on 19 Jul 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-2026-63834 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-2026-63834/ (Markdown: https://insights.sbomify.com/CVE-2026-63834/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-63834
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-63834
- OSV: https://osv.dev/vulnerability/CVE-2026-63834

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-63834/
Summaries are generated and may contain mistakes; the official description above is the record.