CVE-2025-63153: Totolink A7000r Firmware DoS Vulnerability

CVE-2025-63153 Overview

CVE-2025-63153 is a stack-based buffer overflow [CWE-121] affecting the TOTOLink A7000R router running firmware version 9.1.0u.6115_B20201022. The vulnerability resides in the urldecode function, where the ssid parameter is processed without proper bounds checking. A remote unauthenticated attacker can send a crafted HTTP request containing an oversized ssid value to trigger the overflow. Successful exploitation causes the device to crash, resulting in a Denial of Service (DoS) condition. The flaw is reachable over the network without authentication or user interaction, making the affected routers susceptible to disruption by any attacker with network access to the management interface.

Critical Impact
Remote unauthenticated attackers can crash the router by submitting a crafted ssid parameter, disrupting network connectivity for all downstream clients.

Affected Products

TOTOLink A7000R hardware device
TOTOLink A7000R firmware version 9.1.0u.6115_B20201022
Deployments exposing the router web management interface to untrusted networks

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

The vulnerability is a classic stack-based buffer overflow in the router's HTTP request handler. When the device processes a request containing the ssid parameter, it passes attacker-controlled input to the urldecode function. The decoded output is written into a fixed-size stack buffer without validating the length of the input. Writing past the end of this buffer overwrites adjacent stack data, including saved registers and the return address.

The consequence in this specific case is a process crash that takes the affected service offline, producing a Denial of Service condition. Because the vulnerable code path is exposed through the network-facing management interface and requires no authentication, an attacker only needs to reach the router's HTTP service to trigger the condition. Repeated exploitation can keep the device in a continuous reboot or unresponsive state.

Root Cause

The root cause is the absence of input length validation before performing URL decoding on the ssid parameter. The urldecode routine copies decoded bytes into a stack buffer of fixed size, trusting that the caller has constrained the input length. Because TOTOLink's HTTP front-end does not enforce a maximum length on ssid, a long attacker-supplied string overflows the destination buffer. This pattern is consistent with CWE-121 (Stack-based Buffer Overflow).

Attack Vector

The attack is delivered over the network through an HTTP request to the router's management interface. The attacker submits a request that includes an ssid parameter populated with a string exceeding the destination buffer's capacity. The decoding routine processes the long value during request handling and overflows the stack, causing the service to terminate. The vulnerability does not require credentials, session tokens, or any user interaction on the victim side.

No public exploit or proof-of-concept beyond the GitHub Vulnerability Documentation has been published. The vulnerability is not listed on the CISA Known Exploited Vulnerabilities catalog. The EPSS probability is 0.366%.

Detection Methods for CVE-2025-63153

Indicators of Compromise

HTTP requests to the router's management interface containing unusually long ssid parameter values
Repeated, unexpected reboots or unresponsiveness of the TOTOLink A7000R device
Crash entries or watchdog resets in router system logs correlated with inbound HTTP traffic
Loss of network connectivity for clients behind the affected router without a configuration change

Detection Strategies

Inspect HTTP traffic destined for router management interfaces for ssid parameter values exceeding a sensible length threshold
Alert on bursts of HTTP POST or GET requests to administrative endpoints from external or untrusted networks
Correlate router availability monitoring with network-layer traffic to identify DoS attempts targeting the device

Monitoring Recommendations

Forward router syslog output to a centralized log platform and monitor for repeated service crashes
Track availability of SOHO and branch routers through ICMP or SNMP polling to detect outages quickly
Enable network telemetry on upstream switches to capture HTTP traffic patterns directed at management interfaces

How to Mitigate CVE-2025-63153

Immediate Actions Required

Restrict access to the TOTOLink A7000R management interface so it is reachable only from trusted internal networks
Disable remote administration from WAN interfaces if it is currently enabled
Place affected devices behind a firewall that filters inbound HTTP requests to the router
Replace end-of-life or unsupported TOTOLink A7000R units in environments where vendor patches are not available

Patch Information

No vendor advisory or firmware update has been published in the NVD record at the time of writing. Administrators should monitor the TOTOLink support portal for updates addressing firmware version 9.1.0u.6115_B20201022 and apply any released patches promptly. Until a fix is available, compensating controls are required.

Workarounds

Block external access to TCP ports used by the router web interface (commonly 80 and 443) at the perimeter
Apply an access control list permitting management traffic only from designated administrator IP addresses
Segment the router management network from general user and guest VLANs
Replace affected devices with supported alternatives if no firmware update is forthcoming

bash

# Example: restrict router management interface to a single admin host
iptables -A INPUT -p tcp --dport 80 -s 192.0.2.10 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP
iptables -A INPUT -p tcp --dport 443 -s 192.0.2.10 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -j DROP