CVE-2026-1741: EFM ipTIME A8004T RCE Vulnerability

CVE-2026-1741 Overview

A backdoor vulnerability has been identified in EFM ipTIME A8004T firmware version 14.18.2. The vulnerability exists in the httpcon_check_session_url function within the /sess-bin/d.cgi file, which is part of the device's Debug Interface. Manipulation of the cmd argument allows attackers to leverage a hidden backdoor, potentially enabling unauthorized remote access to the affected router. The exploit has been publicly disclosed and may be utilized by threat actors.

Critical Impact

Successful exploitation of this backdoor vulnerability could allow remote attackers to gain unauthorized access to the router, potentially compromising the entire network infrastructure behind the device.

Affected Products

• EFM ipTIME A8004T firmware version 14.18.2
• Potentially other ipTIME router models with similar firmware architecture

Discovery Timeline

• February 2, 2026 - CVE-2026-1741 published to NVD
• February 3, 2026 - Last updated in NVD database

Technical Details for CVE-2026-1741

Vulnerability Analysis

This vulnerability is classified under CWE-912 (Hidden Functionality), indicating the presence of intentional or unintentional backdoor functionality within the router's firmware. The affected component is the Debug Interface, specifically the httpcon_check_session_url function located in /sess-bin/d.cgi. While the attack requires network access and high privileges, successful exploitation grants attackers significant control over the device, potentially affecting confidentiality, integrity, and availability of the router and connected network resources.

The vendor was contacted about this disclosure but did not respond, leaving users without an official patch or mitigation guidance.

Root Cause

The root cause of this vulnerability is hidden functionality (CWE-912) present in the router's Debug Interface. The httpcon_check_session_url function improperly handles the cmd argument, allowing attackers to trigger backdoor functionality that should not be accessible in production firmware. This type of vulnerability often results from leftover development or debugging code that was not properly removed before release, or from intentionally embedded hidden access mechanisms.

Attack Vector

The attack is conducted remotely over the network by targeting the Debug Interface endpoint at /sess-bin/d.cgi. The attacker must manipulate the cmd argument passed to the httpcon_check_session_url function to activate the backdoor functionality. While the CVE data indicates that high privileges are required and the attack complexity is high, the public disclosure of this vulnerability means that exploit details may be available to malicious actors.

The exploitation flow involves:

1. Network access to the router's web management interface
2. Crafting requests to the /sess-bin/d.cgi endpoint
3. Manipulating the cmd parameter to trigger the backdoor
4. Gaining unauthorized access upon successful exploitation

Technical details and proof-of-concept information can be found in the GitHub Issue for CVE-28.

Detection Methods for CVE-2026-1741

Indicators of Compromise

• Unexpected HTTP requests to /sess-bin/d.cgi with unusual cmd parameter values
• Unauthorized configuration changes on the affected router
• Suspicious outbound connections originating from the router
• Unexpected admin sessions or authentication events in router logs

Detection Strategies

• Monitor network traffic for requests targeting the /sess-bin/d.cgi endpoint
• Implement intrusion detection rules to identify manipulation of the cmd parameter
• Review router access logs for unauthorized or suspicious access patterns
• Deploy network monitoring to detect anomalous traffic patterns from router management interfaces

Monitoring Recommendations

• Enable comprehensive logging on the router if available
• Implement network segmentation to isolate router management interfaces
• Use a SIEM solution to aggregate and analyze logs from network devices
• Conduct periodic firmware integrity checks where supported

How to Mitigate CVE-2026-1741

Immediate Actions Required

• Restrict network access to the router's management interface to trusted IP addresses only
• Disable remote management access if not required for operations
• Place the router behind a firewall with strict access controls
• Monitor for any suspicious activity targeting the affected endpoint

Patch Information

At the time of this disclosure, no official patch is available from the vendor. EFM was contacted about this vulnerability but did not respond. Users should monitor the VulDB entry #343640 and vendor channels for any future updates or patches. Consider replacing the affected device with an alternative router from a vendor with a proven security response track record.

Workarounds

• Disable the Debug Interface if possible through router configuration
• Implement network-level access controls to block unauthorized access to /sess-bin/d.cgi
• Use VPN or other secure methods for legitimate remote management needs
• Consider deploying the router behind a firewall appliance with deep packet inspection capabilities

# Example: Restrict management interface access via firewall rules
# Block external access to router management interface
iptables -A INPUT -p tcp --dport 80 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP
iptables -A INPUT -p tcp --dport 443 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -j DROP