CVE-2025-67114: Sercomm SCE4255W Auth Bypass Vulnerability

CVE-2025-67114 Overview

A critical vulnerability exists in the Sercomm SCE4255W (FreedomFi Englewood) small cell firmware that allows remote attackers to derive valid administrative and root credentials using a deterministic credential generation algorithm. The vulnerable component, located at /ftl/bin/calc_f2, uses the device's MAC address as a predictable seed to generate credentials, enabling complete authentication bypass and full device access.

Critical Impact

Remote attackers can calculate valid admin/root credentials from publicly observable MAC addresses, leading to complete device compromise without any authentication.

Affected Products

• Sercomm SCE4255W (FreedomFi Englewood) firmware versions before DG3934v3@2308041842
• FreedomFi small cell devices using affected Sercomm firmware
• 5G/LTE small cell deployments utilizing vulnerable SCE4255W hardware

Discovery Timeline

• 2026-03-19 - CVE CVE-2025-67114 published to NVD
• 2026-03-19 - Last updated in NVD database

Technical Details for CVE-2025-67114

Vulnerability Analysis

This vulnerability stems from a fundamental cryptographic design flaw in how the Sercomm SCE4255W firmware generates administrative credentials. The /ftl/bin/calc_f2 binary implements a deterministic algorithm that derives user credentials based solely on the device's MAC address. Since MAC addresses are often discoverable through network scanning, ARP tables, or even physical device inspection, an attacker with knowledge of the target device's MAC address can compute valid credentials without any prior authentication.

This type of firmware vulnerability is particularly severe in telecommunications equipment like small cells, which often serve as critical network infrastructure. The predictable nature of the credential generation means that even devices deployed in isolated network segments remain vulnerable if their MAC addresses can be obtained.

Root Cause

The root cause of this vulnerability is the use of a deterministic credential generation algorithm that relies on predictable input data (the device MAC address). Rather than using cryptographically secure random number generation or allowing administrators to set unique credentials during provisioning, the firmware calculates credentials using a fixed algorithm. This design pattern—sometimes implemented for manufacturing convenience or simplified device recovery—creates a systemic weakness where knowledge of the algorithm and input parameters grants full administrative access.

Attack Vector

The attack can be executed remotely once an attacker obtains the target device's MAC address. The exploitation process involves:

1. MAC Address Discovery: The attacker identifies the target device's MAC address through network reconnaissance, physical access, or information disclosure
2. Credential Derivation: Using the deterministic algorithm in /ftl/bin/calc_f2 or a reimplementation, the attacker calculates the administrative credentials
3. Authentication Bypass: The derived credentials are used to authenticate to the device's management interface
4. Device Compromise: With administrative or root access, the attacker gains full control over the small cell device

The vulnerability mechanism centers on the calc_f2 binary processing the MAC address through a predictable transformation to generate credentials. For technical details on the algorithm implementation, refer to the Nero Team Blog analysis.

Detection Methods for CVE-2025-67114

Indicators of Compromise

• Unexpected administrative login attempts or successful authentications from unknown IP addresses
• Configuration changes to the small cell device without authorized administrator activity
• Unusual outbound network connections from the small cell infrastructure
• Modifications to firmware or system files on the device

Detection Strategies

• Monitor authentication logs for administrative login patterns, especially from external or unexpected source addresses
• Implement network segmentation monitoring to detect unauthorized access attempts to small cell management interfaces
• Deploy intrusion detection rules to identify reconnaissance activity targeting device MAC addresses
• Audit device configurations periodically to detect unauthorized changes

Monitoring Recommendations

• Enable verbose logging on small cell management interfaces and forward logs to a centralized SIEM
• Monitor network traffic for connections to management ports (SSH, HTTP/HTTPS, Telnet) from non-administrative networks
• Implement alerting for multiple failed authentication attempts followed by a successful login
• Track firmware version information across deployed devices to identify unpatched systems

How to Mitigate CVE-2025-67114

Immediate Actions Required

• Update affected Sercomm SCE4255W devices to firmware version DG3934v3@2308041842 or later immediately
• Restrict network access to device management interfaces using firewall rules and network segmentation
• Conduct an audit of deployed small cell devices to identify units running vulnerable firmware versions
• Review device logs for signs of unauthorized access or credential compromise

Patch Information

Sercomm has addressed this vulnerability in firmware version DG3934v3@2308041842 and later releases. Organizations should coordinate with FreedomFi or their equipment vendor to obtain and deploy the patched firmware. Additional technical documentation is available through the FCC ID Report P27-SCE4255W and the FreedomFi homepage.

Workarounds

• Implement strict network access controls to limit management interface exposure to trusted administrator networks only
• Deploy a VPN or jump host architecture requiring additional authentication before accessing device management
• Consider disabling remote management interfaces entirely and requiring local/console access for administration
• Monitor MAC address exposure through network segmentation and disable unnecessary broadcast protocols

# Example: Network segmentation using iptables to restrict management access
# Allow management access only from trusted admin network
iptables -A INPUT -p tcp --dport 22 -s 10.0.100.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -s 10.0.100.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 22 -j DROP
iptables -A INPUT -p tcp --dport 443 -j DROP