CVE-2025-5156 is a critical buffer overflow vulnerability identified in the H3C GR-5400AX router, specifically affecting versions up to 100R008. The flaw resides in the EditWlanMacList function within the /routing/goform/aspForm file. This function improperly handles the 'param' argument, allowing an attacker to manipulate it in a way that causes a buffer overflow. Such a vulnerability can be exploited remotely without requiring user interaction or prior authentication, as indicated by the CVSS vector (AV:N/AC:L/AT:N/UI:N/PR:L). The buffer overflow can lead to severe consequences including arbitrary code execution with elevated privileges, potentially allowing an attacker to take full control of the affected device. The vendor, H3C, was notified early but has not responded or provided a patch, increasing the risk of exploitation. Although no known exploits have been observed in the wild yet, public disclosure of the exploit code increases the likelihood of imminent attacks. The vulnerability's CVSS 4.0 score is 8.7 (high), reflecting its critical impact on confidentiality, integrity, and availability of the device and connected networks. The H3C GR-5400AX is a widely deployed enterprise-grade router, often used in corporate and service provider environments, making this vulnerability particularly dangerous for network infrastructure security.

For European organizations, the exploitation of CVE-2025-5156 could have significant impacts. Compromise of the H3C GR-5400AX routers can lead to full network compromise, data exfiltration, disruption of network services, and lateral movement within corporate networks. This is especially critical for sectors relying on robust network infrastructure such as finance, telecommunications, government, and critical infrastructure. The ability to remotely execute code without authentication means attackers can bypass perimeter defenses and gain persistent access. Given the lack of vendor response and patches, organizations face increased risk of targeted attacks or opportunistic exploitation by cybercriminals or state-sponsored actors. The disruption or manipulation of network traffic could also impact data privacy compliance under GDPR, leading to regulatory and reputational consequences.

1. Immediate network segmentation: Isolate affected H3C GR-5400AX devices from critical network segments to limit potential lateral movement. 2. Implement strict access controls: Restrict remote management access to trusted IP addresses only and disable unnecessary remote management interfaces. 3. Monitor network traffic: Deploy intrusion detection/prevention systems (IDS/IPS) with signatures or heuristics to detect exploitation attempts targeting the EditWlanMacList function. 4. Apply compensating controls: Use firewall rules to block suspicious HTTP/HTTPS requests targeting the /routing/goform/aspForm endpoint. 5. Vendor engagement: Continuously monitor for vendor patches or advisories and plan immediate patch deployment once available. 6. Incident response readiness: Prepare for potential exploitation by updating incident response plans and conducting tabletop exercises focused on network device compromise. 7. Device replacement: Consider replacing vulnerable devices with alternative hardware if patching is not forthcoming and risk is unacceptable. 8. Firmware integrity checks: Regularly verify firmware integrity and device configurations to detect unauthorized changes.