CVE-2026-3701: H3C Magic B1 Buffer Overflow Vulnerability

CVE-2026-3701 Overview

A buffer overflow vulnerability has been identified in H3C Magic B1 router firmware up to version 100R004. The vulnerability exists in the Edit_BasicSSID_5G function within the /goform/aspForm file, where improper handling of the param argument allows an attacker to trigger a buffer overflow condition. This security flaw can be exploited remotely over the network, potentially allowing attackers to execute arbitrary code or cause denial of service on affected devices.

The exploit details have been publicly disclosed, and the vendor (H3C) was contacted about this vulnerability but did not respond.

Critical Impact
Remote attackers can exploit this buffer overflow to potentially gain unauthorized access to the device, execute malicious code, or disrupt network services managed by the affected H3C Magic B1 router.

Affected Products

H3C Magic B1 Firmware (versions up to 100R004)
H3C Magic B1 Hardware Device

Discovery Timeline

March 8, 2026 - CVE-2026-3701 published to NVD
March 10, 2026 - Last updated in NVD database

Technical Details for CVE-2026-3701

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 Edit_BasicSSID_5G function, which is responsible for handling wireless SSID configuration for the 5GHz band on the H3C Magic B1 router. When processing the param argument, the function fails to properly validate the length of user-supplied input before copying it into a fixed-size buffer in memory.

The network-accessible nature of this vulnerability through the /goform/aspForm endpoint means that any attacker with low-level privileges who can reach the device's web management interface can potentially exploit this flaw. The vulnerability allows for high impact to confidentiality, integrity, and availability of the affected system.

Root Cause

The root cause of this vulnerability is insufficient bounds checking in the Edit_BasicSSID_5G function. When the param argument is processed, the function does not verify that the input data fits within the allocated buffer space. This allows an attacker to supply an oversized input that overflows the buffer boundaries, potentially overwriting adjacent memory regions including return addresses or function pointers.

Attack Vector

The attack can be executed remotely over the network by sending a crafted HTTP request to the /goform/aspForm endpoint. The attacker must have low-level privileges (authenticated access) to the router's management interface. By manipulating the param argument with specially crafted data, the attacker can trigger the buffer overflow condition.

The exploitation process typically involves:

Identifying a vulnerable H3C Magic B1 device with firmware version 100R004 or earlier
Authenticating to the router's web management interface
Sending a malicious request to /goform/aspForm targeting the Edit_BasicSSID_5G function
Including an oversized param value designed to overflow the buffer and potentially gain control of program execution

For detailed technical information about this vulnerability, refer to the GitHub Report Document which contains the publicly disclosed exploit details.

Detection Methods for CVE-2026-3701

Indicators of Compromise

Unusual HTTP POST requests to /goform/aspForm containing abnormally large parameter values
Unexpected router reboots or crashes indicative of buffer overflow exploitation attempts
Anomalous network traffic originating from the router suggesting potential compromise
Modified wireless SSID configurations that were not authorized by administrators

Detection Strategies

Implement network monitoring to detect HTTP requests to /goform/aspForm with payload sizes exceeding normal operational parameters
Configure intrusion detection systems (IDS) to alert on buffer overflow attack patterns targeting H3C devices
Monitor router logs for authentication attempts followed by crashes or unexpected behavior
Deploy web application firewalls (WAF) to filter requests containing potential buffer overflow payloads

Monitoring Recommendations

Enable and centralize logging for all H3C Magic B1 router administrative activities
Implement real-time alerting for any access to the /goform/aspForm endpoint from untrusted sources
Regularly audit network traffic patterns to and from affected router devices
Monitor for firmware integrity changes that could indicate successful exploitation

How to Mitigate CVE-2026-3701

Immediate Actions Required

Restrict access to the router's web management interface to trusted internal networks only
Implement strong firewall rules to prevent external access to the device's administrative ports
Review and audit all user accounts with access to the router management interface
Consider temporarily disabling remote management capabilities until a patch is available

Patch Information

As of the last update, H3C has not responded to vulnerability disclosure attempts and no official patch has been released. Organizations should monitor the VulDB entry and H3C security advisories for future patch releases. Given the lack of vendor response, implementing compensating controls is critical.

Workarounds

Place the H3C Magic B1 router behind a network firewall that restricts access to the management interface
Use network segmentation to isolate the router's management plane from untrusted network segments
Implement access control lists (ACLs) to allow management interface access only from designated administrator IP addresses
Consider replacing vulnerable devices with alternatives from vendors that provide timely security updates

bash

# Example iptables rules to restrict access to router management interface
# Apply on upstream firewall to protect H3C Magic B1 device

# Allow management access only from trusted admin subnet
iptables -A FORWARD -d <router_ip> -p tcp --dport 80 -s 192.168.1.0/24 -j ACCEPT
iptables -A FORWARD -d <router_ip> -p tcp --dport 443 -s 192.168.1.0/24 -j ACCEPT

# Block all other access to management ports
iptables -A FORWARD -d <router_ip> -p tcp --dport 80 -j DROP
iptables -A FORWARD -d <router_ip> -p tcp --dport 443 -j DROP