CVE-2025-26856: UD-LT2 Firmware RCE Vulnerability

CVE-2025-26856 Overview

CVE-2025-26856 is an OS command injection vulnerability [CWE-78] in I-O Data UD-LT2 router firmware version 1.00.008_SE and earlier. The flaw allows an authenticated attacker with administrative credentials to inject arbitrary operating system commands through a specific management screen operation. Successful exploitation leads to arbitrary command execution on the underlying device. This issue is distinct from CVE-2025-20617 and was reported against a different screen operation in the same product line. I-O Data has published support information acknowledging the vulnerability and provides firmware updates to address it.

Critical Impact
An authenticated administrator can execute arbitrary OS commands on the UD-LT2 device, fully compromising confidentiality, integrity, and availability of the router.

Affected Products

I-O Data UD-LT2 firmware version 1.00.008_SE
I-O Data UD-LT2 firmware versions earlier than 1.00.008_SE
I-O Data UD-LT2 LTE router hardware running affected firmware

Discovery Timeline

2025-02-20 - CVE-2025-26856 published to the National Vulnerability Database
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-26856

Vulnerability Analysis

The vulnerability stems from improper neutralization of special elements passed to an OS command interpreter on the UD-LT2 router. A management screen accepts attacker-controlled input and incorporates it into a shell command without adequate sanitization or argument validation. An authenticated administrator can manipulate the request parameters for that screen operation to break out of the intended command context. The injected payload then runs in the privilege context of the firmware's web management process, which on embedded routers typically maps to elevated system privileges. Because the attack surface is the network-exposed web administration interface, exploitation can occur remotely once credentials are obtained or reused.

Root Cause

The firmware constructs OS commands using unsanitized request parameters and passes the resulting string to a shell. Metacharacters such as ;, |, &, backticks, and $() are not neutralized, enabling command chaining. This pattern is the classic OS command injection weakness tracked under [CWE-78].

Attack Vector

An attacker first authenticates to the UD-LT2 web management interface using an administrative account, which may be obtained through credential reuse, weak default credentials, phishing, or prior compromise. The attacker then submits a crafted HTTP request to the affected management screen with shell metacharacters embedded in a vulnerable parameter. The firmware concatenates the input into an OS command and executes it, returning control of the underlying Linux-based router to the attacker. Compromised routers can be used to pivot into internal networks, intercept traffic, or join botnets.

No public proof-of-concept code is available. Refer to the JVN Security Advisory and I-O Data Support Information for vendor-supplied technical details.

Detection Methods for CVE-2025-26856

Indicators of Compromise

Unexpected outbound connections originating from the UD-LT2 device to unknown IP addresses or command-and-control infrastructure
HTTP POST requests to administrative endpoints containing shell metacharacters such as ;, |, &&, backticks, or $()
Configuration changes, new accounts, or modified firewall rules on the router not associated with authorized administrative activity
Unusual DNS queries or traffic patterns sourced from the router's management interface

Detection Strategies

Inspect web management access logs for authenticated sessions submitting requests with embedded shell syntax in parameters
Monitor authentication logs on the router for administrative logins from unexpected source IP addresses or at unusual hours
Correlate router-sourced network flows against baseline traffic to identify command-and-control or data exfiltration patterns

Monitoring Recommendations

Forward router syslog and authentication events to a central SIEM for long-term retention and correlation
Alert on any administrative login to the UD-LT2 from a non-management network segment
Track firmware version inventory continuously to ensure devices remain on patched releases

How to Mitigate CVE-2025-26856

Immediate Actions Required

Upgrade UD-LT2 firmware to the fixed release published in the I-O Data Support Information advisory
Rotate all administrative credentials on UD-LT2 devices and disable any default or shared accounts
Restrict access to the router's web management interface to trusted management VLANs or specific source IP addresses
Audit recent administrative sessions and configuration changes for signs of misuse

Patch Information

I-O Data has released firmware updates addressing CVE-2025-26856. Administrators should consult the I-O Data Support Information page and the JVN Security Advisory for the fixed version number and download instructions. Apply the update to all UD-LT2 units running firmware 1.00.008_SE or earlier.

Workarounds

Disable remote administration over WAN interfaces until the firmware update is applied
Place the device behind a network access control list that limits management access to a dedicated administrative host
Enforce strong, unique administrative passwords and multi-factor authentication on any upstream identity provider used for device access

bash

# Example: restrict management interface access to a single admin host via upstream firewall
iptables -A FORWARD -p tcp -d <UD-LT2-IP> --dport 443 -s <ADMIN-HOST-IP> -j ACCEPT
iptables -A FORWARD -p tcp -d <UD-LT2-IP> --dport 443 -j DROP