# CVE-2024-6640: pf incorrectly matches different ICMPv6 states in the state table

> Attackers can bypass pf firewall rules to trigger ICMPv6 Echo Replies by exploiting state table matching flaws in Neighbor Discovery handling.

- **Severity:** Medium 6.3 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 11 Aug 2024
- **Updated:** 26 Nov 2024
- **Also known as:** GHSA-57cg-pmv4-v925

## What is CVE-2024-6640?

CVE-2024-6640 is a medium-severity vulnerability in FreeBSD, published on 11 Aug 2024. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

In ICMPv6 Neighbor Discovery (ND), the ID is always 0.  When pf is configured to allow ND and block incoming Echo Requests, a crafted Echo Request packet after a Neighbor Solicitation (NS) can trigger an Echo Reply.  The packet has to come from the same host as the NS and have a zero as identifier to match the state created by the Neighbor Discovery and allow replies to be generated.

ICMPv6 packets with identifier value of zero bypass firewall rules written on the assumption that the incoming packets are going to create a state in the state table.

Weakness: CWE-276 (Incorrect Default Permissions)

## Which versions are affected by CVE-2024-6640?


## How do I fix CVE-2024-6640?

No fix has been published for CVE-2024-6640 yet. Limit exposure of the affected software until one is available.

## Is CVE-2024-6640 being exploited?

There is no known exploitation of CVE-2024-6640 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2024-6640 and fix it if it is affected.

What it is: CVE-2024-6640 is a medium-severity vulnerability in FreeBSD, published on 11 Aug 2024. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2024-6640 in the wild and no public exploit code.

Affected product: FreeBSD. 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-2024-6640/ (Markdown: https://insights.sbomify.com/CVE-2024-6640/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2024-6640
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2024-6640
- OSV: https://osv.dev/vulnerability/CVE-2024-6640

---
From sbomify Insights: https://insights.sbomify.com/CVE-2024-6640/
Summaries are generated and may contain mistakes; the official description above is the record.