CVE-2025-6147: Totolink A702r Buffer Overflow Vulnerability

CVE-2025-6147 Overview

CVE-2025-6147 is a buffer overflow vulnerability in TOTOLINK A702R routers running firmware version 4.0.0-B20230721.1521. The flaw resides in the HTTP POST request handler for the /boafrm/formSysLog endpoint. Attackers can manipulate the submit-url argument to trigger memory corruption [CWE-119]. The vulnerability is exploitable remotely over the network and a public proof-of-concept has been disclosed, increasing the risk of opportunistic exploitation against exposed devices.

Critical Impact
Remote attackers with low-privileged access can trigger a buffer overflow in the router's web management interface, potentially leading to arbitrary code execution or denial of service on the affected device.

Affected Products

TOTOLINK A702R hardware router
TOTOLINK A702R firmware version 4.0.0-B20230721.1521
Deployments exposing the embedded web management interface (/boafrm/formSysLog)

Discovery Timeline

2025-06-17 - CVE-2025-6147 published to the National Vulnerability Database
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-6147

Vulnerability Analysis

The vulnerability exists in the request handling logic of the formSysLog CGI endpoint served by the device's embedded boa HTTP server. The handler accepts a submit-url parameter from HTTP POST requests without enforcing length validation before copying the value into a fixed-size stack or heap buffer. An authenticated network attacker can submit a crafted request containing an oversized submit-url value to overrun adjacent memory.

The condition is classified under [CWE-119] (Improper Restriction of Operations within the Bounds of a Memory Buffer). Successful exploitation can corrupt control structures such as saved return addresses or function pointers, enabling arbitrary code execution on the MIPS- or ARM-based router. At minimum, the corruption triggers a service crash and denial of service on the management plane.

Root Cause

The root cause is the absence of bounds checking on user-supplied input within the formSysLog handler. The web server reads the submit-url POST parameter and writes it into a buffer using an unsafe copy operation, such as strcpy or sprintf, without validating the input length against the destination size.

Attack Vector

Exploitation requires network reachability to the router's HTTP management interface and low-privileged authenticated access. The attacker sends a crafted HTTP POST request to /boafrm/formSysLog containing an oversized submit-url field. No user interaction is required. Public proof-of-concept material is available, as documented in the GitHub PoC Repository and VulDB #312622.

The vulnerability mechanism is described in prose only. No verified exploitation code is reproduced here. See the GitHub PoC Code reference for technical detail.

Detection Methods for CVE-2025-6147

Indicators of Compromise

HTTP POST requests to /boafrm/formSysLog containing abnormally long submit-url parameter values
Unexpected reboots, watchdog resets, or boa web server crashes on the TOTOLINK A702R
Outbound connections from the router to unfamiliar hosts following inbound management traffic
New or modified accounts and configuration changes on the device administrative interface

Detection Strategies

Inspect web server and reverse-proxy logs for POST requests targeting formSysLog with payload sizes exceeding expected parameter lengths
Deploy network IDS signatures that flag oversized form fields directed at TOTOLINK management endpoints
Correlate router crash events with preceding HTTP requests to identify exploitation attempts

Monitoring Recommendations

Restrict and monitor administrative HTTP access to the router from trusted management networks only
Forward router syslog data to a centralized logging or SIEM platform for retention and alerting
Alert on repeated authentication events followed by POST traffic to /boafrm/ endpoints

How to Mitigate CVE-2025-6147

Immediate Actions Required

Block external access to the router's HTTP management interface from untrusted networks and the WAN
Change default and weak administrative credentials to reduce the prerequisite of low-privileged access
Audit TOTOLINK A702R devices for firmware version 4.0.0-B20230721.1521 and inventory exposure
Monitor the TOTOLINK Official Site for firmware updates addressing this CVE

Patch Information

At the time of publication no vendor advisory or patched firmware has been listed in the available references. Administrators should track the VulDB #312622 Details entry and the vendor support portal for updates. Until a patch is released, apply the workarounds below.

Workarounds

Disable remote management on the WAN interface and limit LAN-side management to a dedicated VLAN
Place the device behind a firewall that filters HTTP traffic to /boafrm/formSysLog
Replace end-of-life or unsupported router models with vendor-supported alternatives where feasible
Segment IoT and network infrastructure devices from user and server subnets to limit lateral movement

bash

# Example: restrict router management access using an upstream firewall (iptables)
iptables -A FORWARD -p tcp -d <router_ip> --dport 80 -s <trusted_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 <trusted_mgmt_subnet> -j ACCEPT
iptables -A FORWARD -p tcp -d <router_ip> --dport 443 -j DROP