CVE-2026-8764: H3C Magic B3 Buffer Overflow Vulnerability

CVE-2026-8764 Overview

CVE-2026-8764 is a buffer overflow vulnerability affecting H3C Magic B3 routers up to firmware version 100R002. The flaw resides in the UpdateWanParams function within /goform/aspForm, where manipulation of the param argument triggers a memory corruption condition [CWE-119]. The vulnerability is exploitable over the network and has been publicly disclosed. According to the CVE record, the vendor was contacted prior to disclosure but did not respond.

Critical Impact

Authenticated remote attackers can corrupt memory in the router's web management interface by submitting a crafted param value to UpdateWanParams, potentially compromising device confidentiality, integrity, and availability.

Affected Products

• H3C Magic B3 router
• Firmware versions up to 100R002
• Web management interface endpoint /goform/aspForm

Discovery Timeline

• 2026-05-17 - CVE-2026-8764 published to NVD
• 2026-05-18 - Last updated in NVD database

Technical Details for CVE-2026-8764

Vulnerability Analysis

The vulnerability is classified as an Improper Restriction of Operations within the Bounds of a Memory Buffer [CWE-119]. The affected component is the UpdateWanParams handler exposed through the router's HTTP form interface at /goform/aspForm. When the handler processes the param argument, it fails to enforce length or boundary constraints on attacker-supplied input. This allows data to be written beyond the allocated buffer, corrupting adjacent memory.

Buffer overflows in embedded HTTP handlers typically permit denial of service through process crashes and, depending on memory layout and platform protections, may permit control-flow hijacking. The H3C Magic B3 is a consumer-grade router where mitigations such as stack canaries, ASLR, and non-executable memory may be incomplete or absent.

A public exploit has been disclosed through the referenced GitHub CVE Issue Tracker and VulDB Vulnerability #364389. The EPSS probability remains low at 0.038%, but public disclosure raises the practical risk to exposed devices.

Root Cause

The UpdateWanParams function copies the param query/form value into a fixed-size buffer without validating its length. Missing bounds checks on user-controlled input lead to memory corruption when oversized data is supplied. The bug is consistent with patterns seen across H3C and similar SoHo router firmware where strcpy, sprintf, or equivalent unsafe routines handle form inputs directly.

Attack Vector

The attack is performed over the network against the router's web interface. The CVSS 4.0 vector indicates high privileges are required (PR:H), meaning the attacker must hold valid credentials to the management interface. A crafted HTTP POST request to /goform/aspForm invoking UpdateWanParams with an oversized param value triggers the overflow. Routers with management interfaces exposed to untrusted networks face elevated risk.

No verified code examples are available. Refer to the VulDB CTI entry for additional technical context.

Detection Methods for CVE-2026-8764

Indicators of Compromise

• HTTP POST requests to /goform/aspForm containing unusually long param values targeting UpdateWanParams.
• Unexpected reboots, web interface crashes, or watchdog resets on H3C Magic B3 devices.
• Authenticated sessions to the router web UI originating from untrusted source IP addresses.

Detection Strategies

• Inspect web server and HTTP access logs on the router for requests to aspForm with abnormal payload sizes.
• Deploy network IDS/IPS rules that flag HTTP requests to /goform/aspForm with param argument lengths exceeding expected boundaries.
• Correlate device crash events with preceding HTTP traffic to the management interface.

Monitoring Recommendations

• Forward router syslog and HTTP access logs to a centralized log platform for retention and analysis.
• Alert on any external (WAN-side) access to the router management interface.
• Track failed and successful administrative authentications against the router web UI for anomalous patterns.

How to Mitigate CVE-2026-8764

Immediate Actions Required

• Disable WAN-side access to the H3C Magic B3 web management interface and restrict administration to trusted LAN segments only.
• Rotate administrative credentials to ensure no unauthorized account holds privileges required for exploitation.
• Place affected routers behind segmentation controls that block direct internet access to /goform/aspForm.

Patch Information

No vendor patch has been published. According to the CVE record, H3C was contacted prior to public disclosure but did not respond. Monitor the H3C security advisories page and the VulDB Vulnerability #364389 record for future updates.

Workarounds

• Restrict HTTP/HTTPS access to the router management interface using ACLs or firewall rules permitting only specific administrative source addresses.
• Disable remote management features on the router if enabled.
• Consider replacing end-of-life or unsupported H3C Magic B3 devices with actively maintained hardware if no vendor fix becomes available.