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

CVE-2026-6581 Overview

CVE-2026-6581 is a buffer overflow vulnerability affecting H3C Magic B1 routers up to firmware version 100R004. The flaw resides in the SetMobileAPInfoById function within the /goform/aspForm endpoint. Attackers can trigger the overflow by manipulating the param argument supplied to the affected handler. The vulnerability is classified under [CWE-119], improper restriction of operations within the bounds of a memory buffer. Remote exploitation is possible across the network, and a public exploit has been disclosed. According to VulDB, the vendor was contacted early about this disclosure but did not respond.

Critical Impact

Remote attackers with low privileges can corrupt memory on H3C Magic B1 devices through /goform/aspForm, potentially leading to code execution or denial of service on perimeter routing equipment.

Affected Products

• H3C Magic B1 router firmware up to and including 100R004
• Web management interface component /goform/aspForm
• SetMobileAPInfoById handler function

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

The vulnerability is a classic buffer overflow [CWE-119] in the H3C Magic B1 web management binary. The SetMobileAPInfoById function processes form data submitted to the /goform/aspForm endpoint. The handler reads the param argument from the HTTP request without validating its length before copying it into a fixed-size stack or heap buffer. An attacker who controls param can write beyond the allocated buffer boundary. This corrupts adjacent memory structures, including saved return addresses and function pointers on embedded MIPS or ARM SoC firmware typical of consumer routers. The EPSS exploit probability is currently 0.046%, but a public proof-of-concept already exists.

Root Cause

The root cause is missing bounds checking on attacker-controlled input within SetMobileAPInfoById. The function trusts the size of user-supplied form parameters when invoking unsafe string operations such as strcpy or sprintf. No length validation occurs before the destination buffer is written.

Attack Vector

The attack vector is network-based with low attack complexity. An authenticated attacker with low privileges sends a crafted HTTP POST request to /goform/aspForm containing an oversized param value. The malformed request reaches SetMobileAPInfoById, which copies the payload into an undersized buffer. Successful exploitation can yield arbitrary code execution in the context of the web management process, typically running with high privileges on embedded firmware.

The vulnerability mechanism is described in the public disclosure on the GitHub H3Cc Documentation and tracked in VulDB Vulnerability #358216. No verified proof-of-concept code is reproduced here.

Detection Methods for CVE-2026-6581

Indicators of Compromise

• HTTP POST requests to /goform/aspForm containing unusually long param values exceeding expected field lengths
• Web management service crashes, restarts, or watchdog reboots on H3C Magic B1 devices
• Unexpected outbound connections from router management interfaces following inbound administrative traffic
• Anomalous configuration changes to mobile access point settings without corresponding administrative sessions

Detection Strategies

• Deploy network intrusion detection signatures that flag oversized form parameters sent to /goform/aspForm
• Inspect HTTP request bodies for SetMobileAPInfoById invocations carrying payloads above documented field length limits
• Correlate router syslog entries for httpd crashes with concurrent inbound HTTP traffic to identify exploitation attempts

Monitoring Recommendations

• Restrict and log all access to the router web management interface, especially from non-management VLANs
• Forward router logs to a centralized log analytics platform and alert on repeated authentication followed by service crashes
• Monitor for new or unauthorized firmware images, mobile AP profiles, or administrative accounts on affected devices

How to Mitigate CVE-2026-6581

Immediate Actions Required

• Block external access to the H3C Magic B1 web management interface at the network perimeter
• Limit /goform/aspForm access to trusted management subnets through ACLs on upstream switches or firewalls
• Rotate administrative credentials on all affected devices and review existing user accounts for unauthorized additions
• Inventory all H3C Magic B1 devices running firmware up to 100R004 and prioritize them for remediation

Patch Information

No vendor patch is currently available. VulDB reports that H3C was contacted regarding this disclosure but did not respond. Administrators should monitor the H3C product security page for firmware updates and consult VulDB Vulnerability #358216 for status changes.

Workarounds

• Disable remote web management entirely if not required for operations
• Place affected routers behind a dedicated management firewall that filters HTTP requests to /goform/aspForm
• Replace end-of-support or unpatched H3C Magic B1 devices with current, vendor-supported hardware
• Segment the router management plane onto an isolated VLAN accessible only via VPN or jump host

# Example ACL restricting web management access to a trusted subnet
acl number 3010
 rule 10 permit tcp source 10.0.100.0 0.0.0.255 destination-port eq 80
 rule 20 permit tcp source 10.0.100.0 0.0.0.255 destination-port eq 443
 rule 30 deny tcp destination-port eq 80
 rule 40 deny tcp destination-port eq 443
interface GigabitEthernet0/0
 packet-filter 3010 inbound