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Heap-based Buffer OverflowWeakness · CWE-122

CVE-2026-29004

HIGH · 8.1 CVSS v3.1 Published 2026-05-04
Patch available
A vendor patch is available. No clean upgrade release — apply the published patch.
See remediation →
86/100
Remediation priority · High
No privileges Zero-click Patch available

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis
How this class of weakness works · CWE-122

Data overflows a buffer allocated on the heap, corrupting neighbouring heap structures and allocator metadata that a patient attacker can groom into control of execution. It is subtler than a stack overflow but just as dangerous. The fix is validating lengths before every write and using safe allocators and bounded operations.

General guidance for the heap-based buffer overflow class — the official description and references above are authoritative for this specific CVE. Want a bespoke review and a reviewed fix? Ask our team →

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Adjacent
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
High
Availability
High

CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Patch available Apply the vendor patch
Vendor patch github.com →
Recommended fix Moderate confidence

Any BusyBox version after commit 42202bfb1e6ac51fa995beda8be4d7b654aeee2a; check upstream BusyBox releases or your distribution's security advisories for the specific version number containing this fix

  1. 1. Identify the current BusyBox version in use by running `busybox --version` or checking the firmware/package manifest
  2. 2. Obtain a fixed BusyBox release that includes commit 42202bfb1e6ac51fa995beda8be4d7b654aeee2a (the D6_OPT_DNS_SERVERS heap overflow fix)
  3. 3. If building from source, fetch the latest busybox source: `git clone https://github.com/vda-linux/busybox_mirror.git`
  4. 4. Verify the fix commit is present: `git log --oneline | head -n 1` should show commit 42202bf or later
  5. 5. Rebuild the BusyBox binary with the fix applied
  6. 6. Replace the vulnerable udhcpc6 binary on the embedded device or in the firmware
  7. 7. Restart any DHCPv6 client services to ensure the patched binary is loaded
  8. 8. Verify the fix by confirming the version now includes the patch (check release notes or build info)
Caveat Minimal risk - this is a security fix for a bug in existing functionality; no API or behavior changes expected beyond eliminating the buffer overflow

Generated from the published advisory — verify against the referenced sources before acting.

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-29004 in production — separate from our analysis above.

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