CVE-2026-75169 Overview
CVE-2026-75169 is an arbitrary file upload vulnerability in the /cgi-bin/ugwupload.cgi endpoint of MBS-Solutions X-Serie Gateway firmware version V6_00_05. A remote authenticated user with the Admin role can upload files with arbitrary content to hardcoded paths on the device. The flaw is classified under CWE-434: Unrestricted Upload of File with Dangerous Type. Because the gateway exposes network management functionality, successful exploitation can compromise device integrity, confidentiality, and availability. Additional research details are published in the GitHub CVE-2026-75169 Research repository.
Critical Impact
An authenticated Admin can write arbitrary file contents to fixed paths on the gateway, enabling configuration tampering, persistence, and potential code execution on the embedded device.
Affected Products
- MBS-Solutions X-Serie Gateway firmware V6_00_05
- Vulnerable component: /cgi-bin/ugwupload.cgi
- See the MBS Solutions X-Series product page for hardware models running the affected firmware
Discovery Timeline
- 2026-09-04 - CVE-2026-75169 published to NVD
- 2026-09-09 - Last updated in NVD database
Technical Details for CVE-2026-75169
Vulnerability Analysis
The /cgi-bin/ugwupload.cgi handler on the X-Serie Gateway accepts file uploads from authenticated Admin sessions and writes the payload to hardcoded filesystem locations. The handler does not restrict the type, content, or destination of the uploaded file. An attacker who controls or compromises Admin credentials can overwrite gateway configuration files, scripts, or executables reachable from those fixed paths.
Because the destination paths are hardcoded rather than derived from validated user input, exploitation is deterministic. The attacker does not need to guess directory structures or bypass path normalization. Any resource located at the hardcoded target becomes a candidate for tampering.
On embedded network gateways, arbitrary writes of this kind commonly translate into code execution. Overwritten CGI scripts, cron entries, or startup files run with the privileges of the web server or root, giving the attacker persistent control over the device and its traffic.
Root Cause
The root cause is missing validation on the upload handler. ugwupload.cgi neither enforces an allow list of file types nor validates the target path against the authenticated user's scope. The Admin role is trusted to write anywhere the handler is coded to reach, which violates least privilege for a network device management interface.
Attack Vector
Exploitation requires network access to the gateway management interface and valid Admin credentials. The attacker sends a crafted HTTP POST request to /cgi-bin/ugwupload.cgi containing the file payload. The handler writes the payload to its hardcoded destination without content inspection. No user interaction is required beyond the initial authenticated session.
Because the vulnerability is reachable over the network from any host that can reach the management interface, exposure of that interface to untrusted networks materially increases risk. Verified proof-of-concept details are documented in the GitHub CVE-2026-75169 Research repository.
Detection Methods for CVE-2026-75169
Indicators of Compromise
- HTTP POST requests to /cgi-bin/ugwupload.cgi from unexpected source addresses or outside change windows
- Modification timestamps on gateway configuration or CGI files that do not correspond to a scheduled update
- Unexpected outbound connections from the gateway following an upload event
- New or altered scripts in web-root or startup directories on the device
Detection Strategies
- Enable and forward web server access logs from the gateway to a central log platform and alert on requests to ugwupload.cgi
- Correlate Admin authentication events with subsequent upload activity to surface stolen-credential use
- Baseline the file inventory of the gateway and alert on drift from the known-good state
Monitoring Recommendations
- Monitor Admin account logins for anomalous source IPs, session times, and geographies
- Track the volume and size of POST requests to /cgi-bin/ endpoints and alert on outliers
- Watch for changes in device behavior such as new listening services or altered routing after management sessions
How to Mitigate CVE-2026-75169
Immediate Actions Required
- Restrict access to the gateway management interface to a dedicated administrative network or VPN
- Rotate all Admin credentials and enforce strong, unique passwords
- Audit recent access to /cgi-bin/ugwupload.cgi and validate the integrity of configuration and script files
- Contact MBS Solutions for firmware updates or vendor guidance covering V6_00_05
Patch Information
No vendor patch is referenced in the NVD entry at the time of publication. Operators should track vendor communications for firmware releases superseding V6_00_05 and apply updates as soon as they become available.
Workarounds
- Place the gateway management interface behind a firewall that permits only trusted administrative sources
- Disable or block external access to /cgi-bin/ugwupload.cgi at an upstream reverse proxy where feasible
- Limit the number of accounts holding the Admin role and review role assignments regularly
- Monitor for unauthorized configuration changes and maintain offline backups of known-good gateway configurations
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.