# CVE-2026-124740: Busybox: use-after-free of requested_ipv6 in udhcpc6

> A malicious local network DHCPv6 server can crash BusyBox udhcpc6 clients or leak address data via crafted replies.

- **Severity:** Medium 4.3 (`CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Harmful if only installed:** No
- **Needs a specific call:** No
- **Fix available:** No
- **Published:** 11 Nov 2026
- **Updated:** 12 Nov 2026
- **Also known as:** GHSA-9f82-ccff-m2qq

## What is CVE-2026-124740?

CVE-2026-124740 is a medium-severity use after free vulnerability in Red Hat Enterprise Linux 6, published on 11 Nov 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

A flaw was found in BusyBox's udhcpc6 DHCPv6 client. A malicious server on the local network can trigger a use-after-free condition by responding with a crafted Dynamic Host Configuration Protocol for IPv6 (DHCPv6) reply packet lacking usable address options. This issue causes the client to read stale heap memory, which can result in a Denial of Service (DoS) due to an application crash or disclose previously assigned network address data in subsequent discovery requests.

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2026-124740?

An affected version is exposed as installed. No special setting or call is needed.


## How do I fix CVE-2026-124740?

No fix has been published for CVE-2026-124740 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-124740 being exploited?

There is no known exploitation of CVE-2026-124740 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-124740 and fix it if it is affected.

What it is: CVE-2026-124740 is a medium-severity use after free vulnerability in Red Hat Enterprise Linux 6, published on 11 Nov 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-2026-124740 in the wild and no public exploit code.
Exposure: An affected version is exposed as installed. No special setting or call is needed.

Affected product: Red Hat Enterprise Linux 6. 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-2026-124740/ (Markdown: https://insights.sbomify.com/CVE-2026-124740/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-124740
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-124740
- OSV: https://osv.dev/vulnerability/CVE-2026-124740

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-124740/
Summaries are generated and may contain mistakes; the official description above is the record.