CVE-2025-71056: GCOM EPON ONU Auth Bypass Vulnerability

CVE-2025-71056 Overview

CVE-2025-71056 is a critical session hijacking vulnerability affecting GCOM EPON 1GE ONU network devices running firmware version C00R371V00B01. The vulnerability stems from improper session management that allows attackers to execute session hijacking attacks by spoofing the IP address of an authenticated user. This weakness is classified under CWE-290 (Authentication Bypass by Spoofing), indicating a fundamental flaw in how the device validates and maintains user sessions.

EPON (Ethernet Passive Optical Network) ONU (Optical Network Unit) devices are critical components in fiber-to-the-premises (FTTP) network infrastructure, making this vulnerability particularly concerning for telecommunications providers and enterprises relying on passive optical networks.

Critical Impact
Attackers can hijack authenticated sessions on GCOM EPON ONU devices by spoofing IP addresses, potentially gaining unauthorized administrative access to network infrastructure without requiring valid credentials.

Affected Products

GCOM EPON 1GE ONU - Firmware version C00R371V00B01
GCOM H18GN Series GPON ONT/ONU devices (potentially affected, verification required)

Discovery Timeline

2026-02-23 - CVE-2025-71056 published to NVD
2026-02-25 - Last updated in NVD database

Technical Details for CVE-2025-71056

Vulnerability Analysis

This session hijacking vulnerability exists due to the device's reliance on IP addresses as the primary or sole mechanism for session validation. When a legitimate user authenticates to the GCOM EPON 1GE ONU device, the system creates a session that is bound to the user's IP address rather than implementing robust session tokens or additional authentication factors.

The vulnerability allows an attacker positioned on the same network segment or with the ability to spoof source IP addresses to impersonate authenticated users. By crafting network packets with a spoofed source IP address matching that of an authenticated administrator, an attacker can inherit the victim's session privileges without ever providing valid credentials.

This attack vector requires network accessibility to the device and is exploitable remotely without user interaction. The impact is significant as successful exploitation results in high confidentiality and integrity impact, allowing attackers to access sensitive configuration data and potentially modify device settings.

Root Cause

The root cause of CVE-2025-71056 is improper session management implementation (CWE-290). The GCOM EPON 1GE ONU firmware version C00R371V00B01 fails to implement cryptographically secure session tokens and instead relies on easily spoofable network-layer identifiers (IP addresses) to authenticate user sessions.

Properly implemented session management should utilize:

Cryptographically random session tokens
Secure cookie attributes (HttpOnly, Secure, SameSite)
Session binding to multiple factors beyond IP address
Session timeout and invalidation mechanisms

Attack Vector

The attack is network-based and requires an attacker to identify an authenticated user's IP address and spoof their identity. The attack flow involves several stages: first, the attacker must identify when a legitimate administrator is authenticated to the device, which could be accomplished through network traffic analysis or timing attacks. Next, the attacker spoofs the source IP address of the authenticated user in their network requests. Finally, the device accepts the spoofed requests as legitimate, granting the attacker the session privileges of the authenticated user.

This vulnerability does not require any privileges on the target system and can be exploited without user interaction, making it particularly dangerous in environments where the management interface is exposed to untrusted networks.

Detection Methods for CVE-2025-71056

Indicators of Compromise

Multiple simultaneous sessions from the same IP address with conflicting actions or geographic impossibilities
Unusual administrative access patterns or configuration changes from unexpected source addresses
Network traffic anomalies showing duplicate IP addresses or MAC-IP binding inconsistencies
Unexpected session activity during periods when legitimate administrators are not active

Detection Strategies

Implement network monitoring to detect IP spoofing attempts through MAC address validation
Deploy intrusion detection rules to identify authentication bypass attempts targeting ONU devices
Monitor device logs for concurrent administrative sessions from the same source IP
Utilize network flow analysis to identify suspicious traffic patterns to device management interfaces

Monitoring Recommendations

Enable verbose logging on GCOM EPON ONU devices and forward logs to a centralized SIEM
Implement network segmentation to isolate ONU management interfaces from untrusted networks
Deploy network-based anomaly detection to identify IP spoofing attempts
Regularly audit active sessions and administrative access logs for unauthorized access

How to Mitigate CVE-2025-71056

Immediate Actions Required

Restrict management interface access to trusted networks only through VLAN segmentation or firewall rules
Implement network access control lists (ACLs) to limit which IP addresses can reach device management interfaces
Enable MAC address binding where supported to add an additional layer of session validation
Monitor for firmware updates from GCOM that address this vulnerability

Patch Information

As of the last modification date (2026-02-25), no official patch has been referenced in the NVD database. Organizations using affected GCOM EPON 1GE ONU devices should:

Contact GCOM support directly through SZGCOM Homepage for updated firmware
Review the GitHub CVE-Disclosures ReadMe for additional technical details
Implement compensating controls until an official patch is available

Workarounds

Isolate GCOM EPON ONU management interfaces on a dedicated management VLAN inaccessible from user networks
Implement strict ingress filtering at network boundaries to prevent IP spoofing attacks
Deploy a jump host or VPN requirement for administrative access to reduce attack surface
Consider temporarily disabling remote management if not critical to operations

bash

# Example network ACL configuration (device-specific syntax may vary)
# Restrict management access to specific trusted management network
access-list management permit 192.168.100.0/24
access-list management deny any
interface management
  ip access-group management in