CVE-2019-25483: Comtrend AR-5310 Auth Bypass Vulnerability

CVE-2019-25483 Overview

CVE-2019-25483 is a restricted shell escape vulnerability affecting the Comtrend AR-5310 router with firmware version GE31-412SSG-C01_R10.A2pG039u.d24k. This command injection flaw allows local users to bypass command restrictions by leveraging the command substitution operator $( ). Attackers can inject arbitrary commands through the $( ) syntax when passed as arguments to allowed commands like ping, ultimately achieving unrestricted shell access on the affected device.

Critical Impact

Local attackers can escape the restricted shell environment and execute arbitrary commands with elevated privileges, potentially gaining full control over the router and compromising network security.

Affected Products

• Comtrend AR-5310 Router
• Firmware Version: GE31-412SSG-C01_R10.A2pG039u.d24k

Discovery Timeline

• 2026-03-11 - CVE CVE-2019-25483 published to NVD
• 2026-03-12 - Last updated in NVD database

Technical Details for CVE-2019-25483

Vulnerability Analysis

The Comtrend AR-5310 router implements a restricted shell environment intended to limit user access to a predefined set of commands. However, the shell fails to properly sanitize command arguments for shell metacharacters, specifically the command substitution operator $( ). This oversight allows attackers to embed arbitrary commands within arguments passed to permitted commands.

When a user executes an allowed command such as ping with an argument containing $(malicious_command), the shell evaluates the embedded command substitution before processing the outer command. This results in the execution of the attacker's injected command with the same privileges as the shell process, effectively bypassing all intended command restrictions.

Root Cause

The vulnerability stems from improper input validation and insufficient sanitization of user-supplied arguments (CWE-306). The restricted shell implementation fails to filter or escape shell metacharacters, including the $() command substitution syntax, before passing arguments to the underlying system shell for execution. This design flaw allows the shell interpreter to process embedded commands as executable code rather than treating them as literal string arguments.

Attack Vector

This is a local attack vector requiring the attacker to have authenticated access to the router's restricted shell interface. The exploitation process involves:

1. Authenticating to the Comtrend AR-5310 router via CLI (typically via Telnet or SSH)
2. Accessing the restricted shell environment
3. Executing a permitted command (e.g., ping) with a malicious argument containing command substitution
4. The injected command executes with shell privileges, escaping the restricted environment

For example, an attacker could pass $(cat /etc/passwd) as an argument to the ping command, causing the system to execute the embedded cat command and potentially expose sensitive system information. This technique can be extended to spawn an unrestricted shell or execute any arbitrary system command.

Technical details and proof-of-concept information are available in the Exploit-DB #47149 entry and the VulnCheck Advisory.

Detection Methods for CVE-2019-25483

Indicators of Compromise

• Unusual command execution patterns in router logs containing $() or backtick syntax
• Unexpected processes running on the router outside normal operations
• Unauthorized configuration changes or new user accounts
• Evidence of shell escapes in authentication or command history logs

Detection Strategies

• Monitor router CLI sessions for command arguments containing shell metacharacters such as $(, ), or backticks
• Implement logging for all restricted shell command executions and review for anomalous patterns
• Deploy network monitoring to detect unusual outbound connections from the router
• Perform regular firmware integrity checks to identify unauthorized modifications

Monitoring Recommendations

• Enable verbose logging on the Comtrend AR-5310 router if available
• Centralize router logs to a SIEM platform for correlation and alerting
• Monitor for lateral movement attempts originating from the router's IP address
• Implement network segmentation to limit the blast radius of a compromised router

How to Mitigate CVE-2019-25483

Immediate Actions Required

• Restrict physical and network access to the router's management interfaces
• Disable Telnet and use SSH with strong authentication where possible
• Implement network segmentation to isolate management interfaces from untrusted networks
• Review and limit user accounts with access to the router's CLI
• Consider replacing end-of-life or unsupported devices with actively maintained alternatives

Patch Information

No vendor patch information is currently available in the CVE data. Organizations should contact Comtrend directly to inquire about firmware updates that address this vulnerability. If no patch is available, consider the workarounds below and evaluate replacement options for affected devices.

Workarounds

• Disable remote CLI access (Telnet/SSH) if not required for operations
• Implement strict network access controls (ACLs) limiting management interface access to trusted IP addresses only
• Deploy a firewall or VPN to protect router management interfaces from unauthorized access
• Monitor router access logs for suspicious command execution attempts
• Consider deploying an alternative router with active security support if no vendor fix is forthcoming

# Example: Restrict management interface access via firewall rule
# Deny all Telnet access to router management interface
iptables -A INPUT -p tcp --dport 23 -j DROP

# Allow SSH only from trusted management network
iptables -A INPUT -p tcp -s 192.168.100.0/24 --dport 22 -j ACCEPT
iptables -A INPUT -p tcp --dport 22 -j DROP