CVE-2026-6563: H3C Magic B1 Buffer Overflow Vulnerability

CVE-2026-6563 Overview

A buffer overflow vulnerability has been discovered in H3C Magic B1 routers running firmware versions up to 100R004. The vulnerability exists in the SetAPWifiorLedInfoById function within the /goform/aspForm endpoint. An attacker can exploit this flaw by manipulating the param argument, causing a buffer overflow condition that could lead to arbitrary code execution or denial of service on the affected device.

Critical Impact

Remote attackers with low privileges can exploit this buffer overflow vulnerability over the network to potentially compromise the router, execute arbitrary code, and gain full control of the device.

Affected Products

• H3C Magic B1 (firmware versions up to 100R004)

Discovery Timeline

• 2026-04-19 - CVE-2026-6563 published to NVD
• 2026-04-22 - Last updated in NVD database

Technical Details for CVE-2026-6563

Vulnerability Analysis

This vulnerability is classified as CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer). The flaw resides in the SetAPWifiorLedInfoById function, which processes user-supplied input through the param argument without proper bounds checking. When malicious input is submitted to the /goform/aspForm endpoint, the function fails to validate the length of the incoming data before copying it into a fixed-size buffer, resulting in a classic buffer overflow condition.

The vulnerability is remotely exploitable over the network and requires only low-level privileges to trigger. No user interaction is required to exploit this flaw. Successful exploitation could allow an attacker to overwrite adjacent memory regions, potentially corrupting program control flow structures such as return addresses or function pointers, ultimately enabling arbitrary code execution with the privileges of the web server process.

Root Cause

The root cause of this vulnerability stems from insufficient input validation in the SetAPWifiorLedInfoById function. The function does not properly verify the size of the param argument before performing memory operations. This lack of boundary checks allows an attacker to supply oversized input that exceeds the allocated buffer space, triggering memory corruption.

The web form handler at /goform/aspForm accepts user-controllable parameters and passes them directly to the vulnerable function without adequate sanitization or length validation.

Attack Vector

The attack can be initiated remotely over the network by sending a specially crafted HTTP request to the /goform/aspForm endpoint on the affected H3C Magic B1 router. The attacker manipulates the param argument with an oversized payload designed to overflow the target buffer.

An attacker with network access to the router's management interface can craft malicious requests containing excessive data in the param field. When processed by the SetAPWifiorLedInfoById function, the oversized input overflows the buffer boundaries, potentially allowing the attacker to overwrite critical memory structures and hijack program execution flow.

For technical details regarding the exploitation methodology, refer to the GitHub Vulnerability Repository which contains additional information about this vulnerability.

Detection Methods for CVE-2026-6563

Indicators of Compromise

• Unexpected HTTP POST requests to /goform/aspForm containing abnormally large param values
• Router instability, unexpected reboots, or unresponsive web management interface
• Unusual network traffic patterns originating from or directed at the router
• Evidence of unauthorized configuration changes on the device

Detection Strategies

• Monitor web server logs for suspicious requests to /goform/aspForm with oversized parameters
• Implement network intrusion detection rules to identify buffer overflow exploitation attempts targeting H3C devices
• Deploy web application firewall rules to block requests with excessively long parameter values
• Use SentinelOne Singularity to detect anomalous behavior patterns associated with buffer overflow exploitation

Monitoring Recommendations

• Enable verbose logging on the router's web management interface to capture all incoming requests
• Implement network-level monitoring to track traffic destined for router management ports
• Regularly audit router configurations for unauthorized changes that may indicate compromise
• Monitor for unusual outbound connections from the router that could indicate post-exploitation activity

How to Mitigate CVE-2026-6563

Immediate Actions Required

• Restrict network access to the router's management interface to trusted IP addresses only
• Disable remote management access if not strictly required for operations
• Place affected routers behind a firewall that filters requests to /goform/aspForm
• Monitor for firmware updates from H3C and apply patches immediately when available

Patch Information

As of the last update, the vendor (H3C) has not responded to disclosure attempts regarding this vulnerability. No official patch is currently available. Organizations should implement compensating controls and monitor for security updates from H3C. Additional vulnerability details can be found at VulDB #358200 and the VulDB CTI Analysis.

Workarounds

• Implement network segmentation to isolate vulnerable routers from untrusted networks
• Configure access control lists (ACLs) to limit management interface access to specific administrator IP addresses
• Consider replacing vulnerable devices with alternative hardware if the vendor does not provide a timely patch
• Use a reverse proxy or web application firewall to filter and validate incoming requests before they reach the router

# Example iptables rules to restrict management access (apply on upstream firewall)
# Block external access to the router's web management port
iptables -A FORWARD -d <router_ip> -p tcp --dport 80 -j DROP
iptables -A FORWARD -d <router_ip> -p tcp --dport 443 -j DROP

# Allow management access only from trusted admin subnet
iptables -I FORWARD -s 10.0.0.0/24 -d <router_ip> -p tcp --dport 80 -j ACCEPT
iptables -I FORWARD -s 10.0.0.0/24 -d <router_ip> -p tcp --dport 443 -j ACCEPT