Critical OpenWrt DHCPv6 Stack Overflow CVE-2026-53921

Security researchers have disclosed a critical remote code execution vulnerability (CVE-2026-53921) in the OpenWrt router firmware. The stack-based buffer overflow is triggered during the processing of malformed DHCPv6 responses.

This allows an unauthenticated attacker on the local network to execute arbitrary commands with root privileges. Network admins verifying packet filters can scrub logs using the [Data Masking Tool](/tools/data-masking-tool/).

Analyzing the DHCPv6 Buffer Overflow

The overflow occurs because the DHCPv6 client does not validate option lengths before copying payload data to a fixed-size buffer. This allows attackers to overwrite return addresses on the stack.

RCE Threat and Mitigation for Embedded Routers

OpenWrt has released version 25.04.1 containing a fix, and users are urged to flash their devices to prevent potential network compromise.