CVE-2025-63153: Totolink A7000r Firmware DoS Vulnerability

CVE-2025-63153 Overview

CVE-2025-63153 is a stack overflow vulnerability discovered in the TOTOLink A7000R router firmware version V9.1.0u.6115_B20201022. The vulnerability exists within the urldecode function, specifically in how it handles the ssid parameter. This flaw allows remote attackers to trigger a Denial of Service (DoS) condition by sending specially crafted requests to the affected device.

Critical Impact

Remote attackers can exploit this stack overflow vulnerability to crash the TOTOLink A7000R router without authentication, causing network disruption for all connected devices.

Affected Products

• TOTOLink A7000R Firmware version 9.1.0u.6115_B20201022
• TOTOLink A7000R Hardware

Discovery Timeline

• 2025-11-10 - CVE-2025-63153 published to NVD
• 2025-11-17 - Last updated in NVD database

Technical Details for CVE-2025-63153

Vulnerability Analysis

This vulnerability is classified as CWE-121 (Stack-based Buffer Overflow). The flaw resides in the urldecode function of the TOTOLink A7000R router firmware. When processing the ssid parameter, the function fails to properly validate the length of user-supplied input before copying it to a fixed-size stack buffer. This allows an attacker to overflow the stack buffer by providing an overly long or malformed ssid value in a crafted HTTP request.

The vulnerability can be exploited remotely over the network without requiring any authentication or user interaction. While the immediate impact is limited to availability (Denial of Service), stack overflow vulnerabilities in embedded devices can potentially be leveraged for more severe attacks if the execution flow can be controlled.

Root Cause

The root cause of this vulnerability is insufficient input validation in the urldecode function. The function does not properly check the length of the ssid parameter before processing it, allowing data to overflow beyond the allocated stack buffer boundaries. This is a common vulnerability pattern in embedded device firmware where memory-safe programming practices may not be consistently implemented.

Attack Vector

The attack vector is network-based, meaning attackers can exploit this vulnerability remotely without physical access to the device. The exploitation requires:

1. Network access to the TOTOLink A7000R router (either from the LAN or potentially from the WAN if the management interface is exposed)
2. Crafting a malicious HTTP request with an oversized or specially formatted ssid parameter
3. Sending the request to the vulnerable urldecode function endpoint

The vulnerability does not require authentication or user interaction, making it trivially exploitable once network access is established. When triggered, the stack overflow causes the device to crash, resulting in a Denial of Service condition that disrupts network connectivity for all users relying on the router.

Technical details and proof-of-concept information can be found in the GitHub Vulnerability Report.

Detection Methods for CVE-2025-63153

Indicators of Compromise

• Unexpected router reboots or crashes occurring frequently
• Loss of network connectivity without apparent cause
• Unusual HTTP requests targeting the router's web interface containing oversized ssid parameters
• Abnormal traffic patterns directed at the router management interface

Detection Strategies

• Monitor network traffic for HTTP requests to the TOTOLink A7000R web interface containing abnormally long ssid parameter values
• Implement intrusion detection system (IDS) rules to detect buffer overflow attack patterns targeting embedded device management interfaces
• Configure network monitoring to alert on repeated router crashes or unexpected reboots
• Review router access logs for malformed or suspicious requests

Monitoring Recommendations

• Enable logging on the TOTOLink A7000R if available and monitor for crash events
• Deploy network-based monitoring to track traffic destined for the router's management ports
• Consider placing the router management interface behind a firewall or VPN to limit exposure
• Implement SentinelOne Singularity for network visibility to detect anomalous traffic patterns targeting IoT devices

How to Mitigate CVE-2025-63153

Immediate Actions Required

• Restrict access to the TOTOLink A7000R management interface to trusted networks only
• Disable remote management features if not required
• Implement firewall rules to block untrusted access to the router's web interface
• Monitor for vendor firmware updates that address this vulnerability
• Consider network segmentation to isolate the vulnerable device

Patch Information

At the time of publication, no official patch has been released by TOTOLink for this vulnerability. Users should monitor the TOTOLink support website for firmware updates that address CVE-2025-63153. The vulnerability affects firmware version 9.1.0u.6115_B20201022.

Workarounds

• Disable the web management interface if not actively needed
• Restrict management interface access to specific trusted IP addresses using firewall rules
• Place the router management interface on a separate VLAN with restricted access
• If possible, use an alternative router until a patched firmware version is available
• Implement network access controls to limit exposure of the vulnerable endpoint

# Example firewall rule to restrict management interface access (adapt to your firewall)
# Block external access to router management port (typically port 80/443)
iptables -A INPUT -p tcp --dport 80 -s ! 192.168.1.0/24 -j DROP
iptables -A INPUT -p tcp --dport 443 -s ! 192.168.1.0/24 -j DROP