CVE-2025-6733 Overview
CVE-2025-6733 is a buffer overflow vulnerability in the UTT HiPER 840G router firmware up to version 3.1.1-190328. The flaw resides in the sub_416928 function inside the /goform/formConfigDnsFilterGlobal API endpoint. Attackers manipulate the GroupName argument to trigger a buffer overflow [CWE-119]. The vulnerability is remotely exploitable and requires only low-privileged authentication. Public disclosure of the exploit details has occurred, and the vendor did not respond to disclosure attempts, leaving affected devices without an official patch.
Critical Impact
Authenticated remote attackers can overflow stack or heap buffers through the GroupName parameter, potentially leading to arbitrary code execution or full compromise of the router.
Affected Products
- UTT HiPER 840G firmware versions up to and including 3.1.1-190328
- UTT 840G hardware device (version 3.0 confirmed in CPE data)
- UTT 840G firmware (all variants under cpe:2.3:o:utt:840g_firmware)
Discovery Timeline
- 2025-06-26 - CVE-2025-6733 published to NVD
- 2026-01-08 - Last updated in NVD database
Technical Details for CVE-2025-6733
Vulnerability Analysis
The vulnerability exists in the UTT HiPER 840G web management interface. The formConfigDnsFilterGlobal handler processes user-supplied DNS filter group configuration data through an exposed /goform/ endpoint. Internally, the sub_416928 function copies the GroupName parameter into a fixed-size buffer without enforcing length validation. This unchecked copy operation corrupts adjacent memory regions when the input exceeds the destination buffer.
Buffer overflows in MIPS-based small-office routers like the HiPER 840G frequently enable arbitrary code execution. Attackers can overwrite saved return addresses or function pointers to redirect execution flow. Public exploit material has been released through community CVE documentation repositories.
Root Cause
The root cause is improper restriction of operations within the bounds of a memory buffer [CWE-119]. The sub_416928 function fails to validate the length of the GroupName HTTP parameter before performing a buffer copy. UTT did not respond to disclosure outreach, and no patched firmware version has been published.
Attack Vector
The attack is network-reachable through the router's web administration interface. An attacker with valid low-privileged credentials submits a crafted HTTP request to /goform/formConfigDnsFilterGlobal containing an oversized GroupName value. When the device is exposed to untrusted networks or uses default credentials, the attack surface broadens substantially. Successful exploitation results in memory corruption that can be weaponized to execute attacker-controlled code at the privilege level of the web server process.
No verified proof-of-concept code is reproduced here. Refer to the GitHub CVE Documentation for technical details published by the original reporter.
Detection Methods for CVE-2025-6733
Indicators of Compromise
- Unusually long GroupName parameter values in HTTP POST requests targeting /goform/formConfigDnsFilterGlobal
- Unexpected reboots, watchdog resets, or crashes of the HiPER 840G web management daemon
- Outbound connections from the router to unfamiliar IP addresses following administrative HTTP traffic
- Modified DNS filter configuration entries that were not authorized by administrators
Detection Strategies
- Inspect HTTP traffic to the router for requests against /goform/formConfigDnsFilterGlobal with parameter values exceeding typical lengths
- Apply network IDS signatures that match oversized GroupName POST bodies aimed at UTT management endpoints
- Correlate router crash logs and syslog entries with administrative authentication events to identify exploitation attempts
Monitoring Recommendations
- Forward router syslog data to a centralized SIEM for inspection of repeated web management failures
- Alert on any inbound connections to the router's HTTP/HTTPS management ports from outside the management VLAN
- Track configuration drift on UTT devices through periodic configuration backups and diff comparisons
How to Mitigate CVE-2025-6733
Immediate Actions Required
- Restrict access to the router's web management interface to a dedicated management VLAN or trusted IP allowlist
- Disable WAN-side administration if currently enabled, and verify the management port is unreachable from the internet
- Rotate administrator credentials to strong, unique values and remove unused low-privileged accounts
- Evaluate replacement of the UTT HiPER 840G given the vendor's lack of response and absence of a patch
Patch Information
No vendor patch is available. The reporter states that UTT was contacted prior to disclosure but did not respond. Organizations operating the HiPER 840G should treat the device as unsupported for the affected firmware lines and plan migration to a maintained platform.
Workarounds
- Place the device behind an upstream firewall that blocks unsolicited access to the management interface
- Use access control lists on the router to permit administrative HTTP requests only from designated workstations
- Monitor and rate-limit requests to /goform/ endpoints with a reverse proxy or intermediary web application firewall when feasible
- Replace the affected hardware with a vendor-supported alternative if continued internet exposure is required
# Example: restrict inbound access to router management interface using upstream iptables
iptables -A FORWARD -p tcp -d <router_ip> --dport 80 -s <mgmt_subnet> -j ACCEPT
iptables -A FORWARD -p tcp -d <router_ip> --dport 80 -j DROP
iptables -A FORWARD -p tcp -d <router_ip> --dport 443 -s <mgmt_subnet> -j ACCEPT
iptables -A FORWARD -p tcp -d <router_ip> --dport 443 -j DROP
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
