CVE-2025-7118: UTT 840G Firmware Buffer Overflow Flaw

CVE-2025-7118 Overview

CVE-2025-7118 is a buffer overflow vulnerability in the UTT HiPER 840G router firmware up to version 3.1.1-190328. The flaw resides in the /goform/formPictureUrl handler, where the importpictureurl parameter is processed without proper bounds checking. Attackers can trigger memory corruption remotely over the network with low privileges. The exploit has been publicly disclosed, increasing the risk of opportunistic exploitation. The vendor was contacted before disclosure but did not respond, leaving affected devices without an official patch. The vulnerability is tracked under CWE-119 for improper restriction of operations within memory buffers.

Critical Impact

Remote attackers with low-privileged access can corrupt memory in the HiPER 840G web management interface, leading to potential denial of service or arbitrary code execution on the device.

Affected Products

• UTT HiPER 840G firmware versions up to 3.1.1-190328
• UTT HiPER 840G hardware revision 3.0
• Any deployment exposing the /goform/formPictureUrl endpoint to untrusted networks

Discovery Timeline

• 2025-07-07 - CVE-2025-7118 published to the National Vulnerability Database
• 2026-01-08 - Last updated in NVD database

Technical Details for CVE-2025-7118

Vulnerability Analysis

The vulnerability affects the web-based management interface of the UTT HiPER 840G enterprise router. The /goform/formPictureUrl form handler accepts the importpictureurl argument from HTTP requests and copies the supplied value into a fixed-size memory buffer. Because the firmware does not validate the length of the input, an oversized value overflows the destination buffer and overwrites adjacent memory.

Successful exploitation can crash the HTTP service, destabilize the router, or allow attackers to overwrite control data such as return addresses. On embedded MIPS or ARM devices without modern memory protections, this class of flaw frequently leads to arbitrary code execution as the web server process, which typically runs with elevated privileges on consumer and SMB routers.

The vulnerability carries an EPSS probability of 1.49%, placing it in the 81st percentile of vulnerabilities by predicted exploitation likelihood.

Root Cause

The root cause is the absence of length validation on the importpictureurl parameter before it is copied into a stack or heap buffer inside the formPictureUrl handler. This is a classic CWE-119 improper restriction of operations within the bounds of a memory buffer. The firmware lacks defensive coding practices such as bounded string copies, input length checks, or stack canaries that would mitigate overflow exploitation.

Attack Vector

Attackers send a crafted HTTP request to the /goform/formPictureUrl endpoint containing an oversized importpictureurl value. The attack requires network access to the management interface and a low-privileged authenticated session. Routers exposing the web UI to the WAN or to broad internal network segments are most at risk. Refer to the GitHub CVE Overview and VulDB #315029 for additional technical details.

No verified exploit code is reproduced here. The vulnerability mechanism involves submitting an HTTP POST request to /goform/formPictureUrl where the importpictureurl parameter exceeds the fixed buffer size allocated by the firmware, overwriting adjacent memory in the web server process.

Detection Methods for CVE-2025-7118

Indicators of Compromise

• HTTP requests to /goform/formPictureUrl containing unusually long importpictureurl parameter values
• Repeated crashes or unexpected restarts of the router's HTTP management service
• Web management interface becoming unresponsive following targeted traffic
• Outbound connections from the router to unfamiliar hosts after suspected exploitation

Detection Strategies

• Inspect web server and access logs on the router for POST requests to /goform/formPictureUrl with importpictureurl values exceeding expected URL length
• Deploy network intrusion detection signatures that flag oversized parameter values targeting formPictureUrl
• Correlate router crash events with preceding HTTP requests to identify probable exploitation attempts

Monitoring Recommendations

• Forward router syslog and HTTP access logs to a centralized analytics platform for retention and querying
• Alert on management interface access from unexpected source addresses, particularly external networks
• Monitor for configuration changes or new administrative sessions following anomalous HTTP traffic patterns

How to Mitigate CVE-2025-7118

Immediate Actions Required

• Restrict access to the router's web management interface to a trusted management VLAN or specific administrator IP addresses
• Disable WAN-side access to the management interface if it is currently exposed to the internet
• Rotate administrator credentials to limit the population of accounts that can reach the vulnerable endpoint
• Inventory all UTT HiPER 840G devices running firmware versions up to 3.1.1-190328 and prioritize them for compensating controls

Patch Information

No vendor patch has been published. According to the disclosure, UTT was contacted before public release but did not respond. Organizations should monitor the vendor's support channels for future firmware updates and consider replacement of unsupported devices if no fix is forthcoming.

Workarounds

• Place the router's management interface behind a firewall rule that allows only specific trusted source addresses
• Use a jump host or VPN for any administrative access to the device, eliminating direct exposure of /goform/formPictureUrl
• Evaluate replacing the HiPER 840G with a supported platform that receives active security maintenance
• Apply web application firewall rules upstream of the device to drop requests with oversized importpictureurl parameters

# Example iptables rule restricting management access to a trusted subnet
iptables -A INPUT -p tcp --dport 80 -s 10.10.0.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP
iptables -A INPUT -p tcp --dport 443 -s 10.10.0.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -j DROP