CVE-2026-75161: MBS-Solutions X-Serie Gateway RCE Vulnerability

CVE-2026-75161 Overview

CVE-2026-75161 is a command injection vulnerability in the ugw-restart method of /cgi-bin/wwwugw.cgi in MBS-Solutions X-Serie Gateway firmware version V6_00_05. A remote authenticated user holding only the low-privileged Standard role can inject arbitrary commands into the dpcheck system utility. Because dpcheck runs as root, successful exploitation yields full root-level code execution on the gateway. The flaw maps to CWE-77: Improper Neutralization of Special Elements used in a Command and carries a network attack vector with low privilege requirements.

Critical Impact

Any authenticated Standard-role user can escalate to root on affected X-Serie Gateway devices, compromising confidentiality, integrity, and availability of the gateway and downstream network segments.

Affected Products

• MBS-Solutions X-Serie Gateway firmware V6_00_05
• Product line reference: MBS Solutions XSeries
• Vendor reference: MBS Solutions Overview

Discovery Timeline

• 2026-09-04 - CVE-2026-75161 published to NVD
• 2026-09-09 - Last updated in NVD database
• Public research repository: GitHub CVE-2026-75161 Research

Technical Details for CVE-2026-75161

Vulnerability Analysis

The vulnerable code path lives inside the ugw-restart handler of the CGI binary /cgi-bin/wwwugw.cgi. This handler invokes the dpcheck system utility using user-influenced input without adequate neutralization of shell metacharacters. Because the CGI process executes dpcheck as root, injected commands inherit root privileges on the gateway operating system.

An attacker only needs credentials for the Standard role, which is the lowest privilege tier exposed by the web management interface. This drastically lowers the bar compared to admin-only flaws. Successful exploitation grants full control of the gateway, including firmware modification, credential theft, traffic interception, and pivoting into segments the gateway routes.

Root Cause

The root cause is improper neutralization of special elements passed to an OS command [CWE-77]. The ugw-restart code path concatenates or passes attacker-controlled parameters into a shell invocation of dpcheck without applying strict allow-list validation, argument arrays, or shell-metacharacter escaping. Standard shell separators such as ;, &&, |, and backticks are honored by the underlying interpreter, enabling arbitrary command execution.

Attack Vector

Exploitation requires network reachability to the gateway management interface and a valid session for a Standard-role account. The attacker submits a crafted request to /cgi-bin/wwwugw.cgi invoking the ugw-restart method with a payload that embeds shell metacharacters in a parameter consumed by the dpcheck invocation. Refer to the public research repository for technical details of the request structure and parameter names. No verified proof-of-concept code is reproduced here.

Detection Methods for CVE-2026-75161

Indicators of Compromise

• Unexpected HTTP POST requests to /cgi-bin/wwwugw.cgi invoking the ugw-restart method from Standard-role sessions.
• Presence of shell metacharacters such as ;, |, &&, $(, or backticks within CGI request parameters targeting dpcheck.
• New or unexpected root-owned processes, cron entries, or SSH keys appearing on the gateway shortly after a ugw-restart request.
• Outbound connections from the gateway to unfamiliar hosts following administrative UI activity.

Detection Strategies

• Inspect web server and CGI access logs on the gateway for ugw-restart invocations correlated with non-administrative user IDs.
• Alert on HTTP request bodies or query strings containing shell metacharacters directed at /cgi-bin/wwwugw.cgi.
• Baseline the expected process tree of wwwugw.cgi and flag child processes other than dpcheck executed with default arguments.

Monitoring Recommendations

• Forward gateway syslog, web access logs, and authentication logs to a centralized analytics platform for correlation.
• Monitor for privilege changes, new local accounts, and firmware integrity deviations on X-Serie devices.
• Track authentication events for Standard-role accounts and alert on anomalous session locations or times.

How to Mitigate CVE-2026-75161

Immediate Actions Required

• Restrict management-interface access to trusted administrative networks using firewall rules or VPN gating.
• Audit and disable unused Standard-role accounts, and rotate credentials for all remaining accounts.
• Enforce strong, unique passwords and, where supported, multi-factor authentication for the gateway UI.
• Review gateway configuration and logs for signs of prior ugw-restart abuse before re-exposing the device.

Patch Information

No vendor patch is referenced in the NVD entry at the time of publication. Administrators should consult MBS-Solutions directly for firmware updates superseding V6_00_05 and apply them once available. Refer to the MBS Solutions XSeries product page for vendor contact and support details.

Workarounds

• Block external access to /cgi-bin/wwwugw.cgi at an upstream reverse proxy or firewall when possible.
• Limit web administration to a dedicated management VLAN reachable only by administrator workstations.
• Remove or downgrade Standard-role accounts that do not require gateway configuration access.
• Increase logging verbosity on the gateway and forward events to an external SIEM for tamper-resistant retention.