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CVE-2026-53921 is a critical Remote Code Execution vulnerability residing within the DHCPv6 service daemon of OpenWrt routers.
The flaw arises due to improper handling and insufficient bounds checking of incoming DHCPv6 packets processed over UDP port 547.
An unauthenticated remote attacker situated on the local network or capable of reaching the interface can transmit a crafted packet.
When the daemon parses this malicious packet, a buffer overflow condition is triggered within the memory allocation routines.
Because odhcpd typically operates with elevated root privileges to manage network interfaces, memory corruption allows arbitrary code execution.
The vulnerability requires no prior authentication, credentials, or user interaction, granting an attacker immediate full control.
During normal operations, the DHCPv6 server listens for solicitations, requests, and reply messages from clients configuring IPv6 addresses.
If an attacker injects machine code or executes return-oriented programming chains via the heap corruption flaw, pointers redirect.
This flaw bypasses standard security layers, allowing malicious payloads to spawn reverse shells or install backdoors onto flash storage.
The attack surface is wide because IPv6 support is enabled by default across numerous consumer and enterprise network routers.
Security researchers discovered that the lack of rigorous input validation on variable option fields allows payload delivery.
Consequently, automated scanning tools can identify and compromise vulnerable endpoints across wide network ranges within milliseconds.
The technical root cause involves unsafe pointer arithmetic when copying option data into fixed-size stack or heap buffers.
Exploitation does not leave immediate logs in standard syslogs unless kernel-level exploit mitigations intercept the crash event.
Once the process crashes and restarts or the malicious payload takes over execution threads, the router joins a botnet.
The severity score is rated at 9.8 out of 10, placing it in the highest criticality tier for embedded systems.
Upgrading firmware packages immediately is the only definitive way to neutralize the flaw before actors weaponize scripts.
Network administrators must audit DHCPv6 exposure immediately and apply vendor-supplied patches across all active deployment nodes.
Advanced persistence can be achieved by writing modifications into overlay filesystems before watchdog daemons detect anomalies.
Memory protection mechanisms can sometimes mitigate direct stack overflows, but heap layout manipulation remains highly effective.
Testing environments confirm that exploitation requires only a single malformed packet sent to the listening UDP socket.
No interaction from network operators or administrators is needed to trigger the vulnerable parsing code path.
Fuzzing campaigns targeting router DHCP daemons frequently uncover similar memory safety issues in legacy C codebases.
Mitigation requires strict adherence to memory-safe programming paradigms or complete replacement of vulnerable parsing functions.
Comprehensive network monitoring of UDP port 547 traffic is essential for detecting exploitation attempts in real time.
Isolation of IPv6 management planes prevents external unauthenticated entities from interacting with vulnerable daemon routines.
DailyCVE Form:
Platform: OpenWrt dhcpv6
Version: Up to 24
Vulnerability: Root RCE
Severity: Critical risk
date: July 2026
Prediction: July 2026
What Undercode Say:
Check dhcpv6 service status
ubus call service list
Inspect odhcpd process execution
ps | grep odhcpd
Verify active firmware version
cat /etc/openwrt_release
Exploit: (Educational Purposes!)
Send crafted UDP packet to port 547
python3 -c “import socket; s = socket.socket(socket.AF_INET6, socket.SOCK_DGRAM); s.sendto(b’\x00′ 1024, (‘ff02::1%eth0’, 547))”
Protection: from this CVE
Update package lists and upgrade odhcpd
opkg update && opkg upgrade odhcpd
Disable external DHCPv6 server exposure on WAN
uci set dhcp.wan.ignore=1 && uci commit dhcp
Impact:
Full root compromise of the router operating system, enabling attackers to intercept traffic, redirect DNS queries, and pivot into internal trusted local area networks without authentication.
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Sources:
Reported By: github.com
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