CVE-2026-6581: H3C Magic B1 Buffer Overflow Vulnerability

CVE-2026-6581 Overview

A buffer overflow vulnerability has been identified in H3C Magic B1 routers running firmware versions up to 100R004. The vulnerability exists in the SetMobileAPInfoById function within the /goform/aspForm file. By manipulating the param argument, an attacker can trigger a buffer overflow condition that may lead to remote code execution or denial of service.

Critical Impact

This remotely exploitable buffer overflow vulnerability allows authenticated attackers to compromise H3C Magic B1 routers, potentially leading to complete device takeover, network infiltration, or service disruption. A public exploit is available, increasing the risk of active exploitation.

Affected Products

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

Discovery Timeline

• 2026-04-19 - CVE-2026-6581 published to NVD
• 2026-04-22 - Last updated in NVD database

Technical Details for CVE-2026-6581

Vulnerability Analysis

This vulnerability is classified under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer). The flaw resides in the SetMobileAPInfoById function, which fails to properly validate the length of user-supplied input before copying it into a fixed-size buffer. When an attacker provides an oversized value for the param argument through the web interface endpoint /goform/aspForm, the function writes beyond the allocated buffer boundaries.

The network-accessible nature of this vulnerability, combined with low attack complexity requirements, makes it particularly dangerous for organizations deploying affected H3C Magic B1 devices. The vulnerability requires low-level privileges to exploit but does not require user interaction, meaning an authenticated attacker can directly target vulnerable devices.

Root Cause

The root cause of this vulnerability is improper bounds checking in the SetMobileAPInfoById function. The function processes user input from the param argument without validating that the input length does not exceed the destination buffer's allocated size. This lack of input validation allows memory corruption when oversized data is processed, potentially overwriting adjacent memory regions including return addresses or function pointers.

Attack Vector

The attack is conducted remotely over the network by sending a specially crafted HTTP request to the /goform/aspForm endpoint. The attacker must have low-level authentication credentials to access the vulnerable function. The exploitation process involves:

1. Authenticating to the H3C Magic B1 web interface
2. Sending a malicious request to /goform/aspForm targeting the SetMobileAPInfoById function
3. Including an oversized payload in the param argument designed to overflow the buffer
4. Achieving code execution or causing a denial of service condition

The vulnerability mechanism involves memory corruption through improper buffer boundary handling. When the SetMobileAPInfoById function receives an excessively long param value, it copies the data into a stack or heap buffer without verifying the input length. This allows an attacker to overwrite critical memory structures. For detailed technical analysis, see the GitHub H3C Documentation and VulDB Vulnerability #358216.

Detection Methods for CVE-2026-6581

Indicators of Compromise

• Unusual HTTP POST requests to /goform/aspForm containing abnormally large param values
• Device crashes or unexpected reboots following web management interface access
• Anomalous network traffic patterns originating from the H3C Magic B1 device
• Unexpected modifications to device configuration or firmware

Detection Strategies

• Monitor web server logs for requests to /goform/aspForm with excessively long parameter values
• Implement network intrusion detection rules to identify buffer overflow exploitation attempts targeting H3C devices
• Deploy SentinelOne agents on network segments containing vulnerable devices to detect post-exploitation activity
• Configure alerting for authentication attempts followed by suspicious requests to vulnerable endpoints

Monitoring Recommendations

• Enable verbose logging on H3C Magic B1 devices to capture all web management interface requests
• Implement network segmentation to isolate IoT and network infrastructure devices from critical systems
• Deploy continuous vulnerability scanning to identify unpatched H3C devices in the environment

How to Mitigate CVE-2026-6581

Immediate Actions Required

• Restrict network access to the H3C Magic B1 web management interface to trusted IP addresses only
• Implement strong authentication controls and disable default credentials
• Place affected devices behind a firewall with strict ingress filtering
• Monitor devices for signs of compromise while awaiting a vendor patch

Patch Information

As of the last update on 2026-04-22, the vendor (H3C) has not released a security patch for this vulnerability. According to the vulnerability disclosure, the vendor was contacted early about this issue but did not respond. Organizations should monitor H3C's official security advisories for patch availability. Additional technical details are available through VulDB Submission #790977.

Workarounds

• Disable remote management access to the device if not required for operations
• Implement network access control lists (ACLs) to restrict access to the /goform/aspForm endpoint
• Consider replacing affected devices with alternative solutions if no patch becomes available
• Deploy a web application firewall (WAF) in front of the device to filter malicious requests

# Example: Restrict management interface access via iptables on upstream device
iptables -A FORWARD -d <H3C_DEVICE_IP> -p tcp --dport 80 -s <TRUSTED_ADMIN_IP> -j ACCEPT
iptables -A FORWARD -d <H3C_DEVICE_IP> -p tcp --dport 80 -j DROP
iptables -A FORWARD -d <H3C_DEVICE_IP> -p tcp --dport 443 -s <TRUSTED_ADMIN_IP> -j ACCEPT
iptables -A FORWARD -d <H3C_DEVICE_IP> -p tcp --dport 443 -j DROP