CVE-2025-48416: OpenSSH Authentication Bypass Vulnerability

CVE-2025-48416 Overview

CVE-2025-48416 is a hardcoded credentials vulnerability affecting firmware that runs an OpenSSH daemon on TCP port 22. The vulnerability stems from a hard-coded entry in the /etc/shadow file for the root user. While the default SSH configuration has PermitRootLogin disabled, this security control can be bypassed or changed by an attacker through multiple attack paths, potentially allowing unauthorized root access to affected devices.

Critical Impact

Attackers who successfully bypass the SSH configuration restrictions can gain root-level access to affected systems using hardcoded credentials, leading to complete device compromise.

Affected Products

• Firmware images containing OpenSSH daemon with hardcoded root credentials
• Devices with the vulnerable /etc/shadow configuration
• Systems where SSH configuration can be modified through alternative attack vectors

Discovery Timeline

• 2025-05-21 - CVE-2025-48416 published to NVD
• 2025-11-03 - Last updated in NVD database

Technical Details for CVE-2025-48416

Vulnerability Analysis

This vulnerability is classified under CWE-912 (Hidden Functionality), which indicates the presence of undocumented or hidden capabilities that can be exploited by attackers. The core issue lies in the firmware design where static credentials are embedded directly into the system image.

The firmware ships with a hardcoded password hash for the root account stored in /etc/shadow. Although the developers attempted to mitigate remote root access by setting PermitRootLogin to disabled in the SSH configuration, this defense-in-depth measure is insufficient. Multiple attack paths exist that allow adversaries to either modify the SSH configuration or leverage the hardcoded credentials through alternative means.

The network-accessible attack vector combined with the potential for complete system compromise makes this a significant security risk for any deployment of affected firmware.

Root Cause

The root cause of this vulnerability is the inclusion of hardcoded credentials in the firmware image combined with insufficient protection of the SSH configuration. Embedding static credentials in firmware is a dangerous practice because:

1. The credentials cannot be changed without a firmware update
2. Once discovered, the credentials affect all deployed instances of the firmware
3. The credentials persist even after device resets

The reliance on a configuration setting (PermitRootLogin) as the sole protection against credential abuse is inadequate when attackers can modify or bypass this configuration through other system vulnerabilities.

Attack Vector

The attack requires network access to the target device running the OpenSSH daemon on port 22. While direct root login via SSH is disabled by default, an attacker can potentially:

1. Exploit other vulnerabilities in the system to gain initial access
2. Modify the SSH configuration to enable PermitRootLogin
3. Authenticate as root using the hardcoded credentials from the /etc/shadow file

Alternatively, if the attacker can obtain the hardcoded password hash from the firmware image, offline password cracking could reveal the plaintext password for use in other attack scenarios.

The vulnerability involves hardcoded credentials in /etc/shadow and a bypassable SSH configuration. When an attacker gains the ability to modify the sshd_config file, they can enable root login and authenticate using the static credentials embedded in the firmware. See the SEC Consult Security Advisory for detailed technical analysis.

Detection Methods for CVE-2025-48416

Indicators of Compromise

• Unexpected SSH connection attempts to TCP port 22 from unauthorized IP addresses
• Successful root authentication events in system logs when root login should be disabled
• Modifications to /etc/ssh/sshd_config enabling PermitRootLogin
• Changes to the SSH daemon configuration or service status

Detection Strategies

• Monitor SSH authentication logs for root login attempts or successful authentications
• Implement file integrity monitoring on /etc/ssh/sshd_config and /etc/shadow
• Deploy network-based intrusion detection to identify SSH brute force or authentication anomalies
• Audit SSH daemon configuration settings during regular security assessments

Monitoring Recommendations

• Configure centralized logging for all SSH authentication events
• Set up alerts for any configuration changes to SSH-related files
• Monitor for firmware extraction attempts or unauthorized access to the file system
• Track network connections to port 22 and correlate with expected administrative access patterns

How to Mitigate CVE-2025-48416

Immediate Actions Required

• Restrict network access to the SSH port (TCP 22) using firewall rules or network segmentation
• Implement strong access controls limiting which IP addresses can reach affected devices
• Monitor affected systems for signs of compromise or unauthorized access attempts
• Contact the device vendor for information on firmware updates addressing this vulnerability

Patch Information

Consult the SEC Consult Security Advisory and the Full Disclosure Mailing List Post for vendor-specific patch information and remediation guidance. Organizations should prioritize obtaining and applying firmware updates that remove the hardcoded credentials and implement proper credential management.

Workarounds

• Block external access to TCP port 22 at the network perimeter
• Implement network segmentation to isolate affected devices from untrusted networks
• Deploy jump hosts or bastion servers to control and audit administrative access
• Consider disabling the SSH service entirely if remote management is not required

# Configuration example - Restrict SSH access via iptables
# Allow SSH only from trusted management network
iptables -A INPUT -p tcp --dport 22 -s 10.0.0.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 22 -j DROP

# Alternatively, disable SSH service if not required
systemctl stop sshd
systemctl disable sshd