CVE-2026-53921 openwrt CVE debrief

Who should care

Defenders responsible for OpenWrt deployments should assess exposure and prioritize patching or mitigating this vulnerability. This includes operators managing OpenWrt-based systems, platform administrators, vulnerability management teams, and security teams responsible for ensuring the security and integrity of their infrastructure.

Why it matters

This vulnerability allows for potential code execution via a stack buffer overflow in the DHCPv6 IA response handler of odhcpd. Defenders responsible for OpenWrt deployments should assess exposure and prioritize patching or mitigating this vulnerability, as it can lead to elevation of privileges and disruption of DHCPv6 services on affected systems.

• Potential code execution via stack buffer overflow
• Unauthenticated access to vulnerable systems
• Elevation of privileges for attackers
• Disruption of DHCPv6 services on affected systems

Technical summary

The odhcpd DHCPv6 IA response handler writes past the end of a fixed 512-byte stack buffer (pdbuf) when a single DHCPv6 REQUEST carries enough IA options to nearly exhaust the reply space. Two independent overflow sites exist in the same call chain, both reachable from the network via a single unauthenticated UDP packet. This issue occurs in the DHCPv6 IA response handler of odhcpd, a DHCPv6, DHCPv4, and router-advertisement server used by OpenWrt. The issue has been patched in version 25.12. Embedded targets often lack stack canaries and ASLR, making code execution realistic. odhcpd runs as root on OpenWrt.

Defensive priority

Defenders should prioritize patching or mitigating this vulnerability, as it can lead to potential code execution.

Recommended defensive actions

• Patch odhcpd to version 25.12 or later
• Restrict access to the odhcpd service to trusted networks or hosts
• Monitor for suspicious DHCPv6 traffic
• Review compensating controls for exposed systems while remediation is scheduled and verified
• Check relevant monitoring, detection, and logs for exposed assets that need extra review
• Track exceptions, retest remediated assets, and close the item only after evidence is documented
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up

Evidence notes

The vulnerability is caused by a stack buffer overflow in the DHCPv6 IA response handler. The issue occurs when a single DHCPv6 REQUEST carries enough IA options to nearly exhaust the reply space, causing the handler to write past the end of a fixed 512-byte stack buffer.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.