CVE-2025-3664 Overview
CVE-2025-3664 is an improper access control vulnerability in the TOTOLINK A3700R router running firmware version 9.1.2u.5822_B20200513. The flaw resides in the setWiFiEasyGuestCfg function within /cgi-bin/cstecgi.cgi, which handles guest Wi-Fi configuration requests. Remote attackers can invoke this function without proper authorization checks, allowing modification of guest wireless settings over the network. The vendor was contacted about this issue but did not respond, and the exploit details have been publicly disclosed. The vulnerability is categorized under [CWE-266] (Incorrect Privilege Assignment).
Critical Impact
Unauthenticated remote attackers can manipulate guest Wi-Fi configuration on affected TOTOLINK A3700R devices through the exposed CGI endpoint.
Affected Products
- TOTOLINK A3700R router hardware
- TOTOLINK A3700R firmware version 9.1.2u.5822_B20200513
- Deployments exposing the /cgi-bin/cstecgi.cgi interface to untrusted networks
Discovery Timeline
- 2025-04-16 - CVE-2025-3664 published to NVD
- 2026-06-17 - Last updated in NVD database
Technical Details for CVE-2025-3664
Vulnerability Analysis
The TOTOLINK A3700R exposes administrative functions through the cstecgi.cgi binary, which dispatches requests to internal handlers based on the topicurl parameter. The setWiFiEasyGuestCfg handler processes guest Wi-Fi configuration but fails to enforce proper authorization checks on the caller. An attacker with network access to the router's web interface can send crafted HTTP requests that reach this handler and alter guest wireless settings without holding administrative credentials. The vulnerability is classified as improper access control under [CWE-266], reflecting incorrect privilege assignment at the CGI dispatch layer. The current EPSS probability for exploitation is approximately 0.53%.
Root Cause
The root cause is the absence of session validation and privilege enforcement before executing the setWiFiEasyGuestCfg routine. The CGI handler trusts the incoming request without verifying that the caller has authenticated as an administrator. This pattern is common across multiple set*Cfg functions in the TOTOLINK CGI binary, which historically bundle authentication logic inconsistently across handlers.
Attack Vector
Exploitation requires network reachability to the router's management interface. An attacker sends an HTTP POST request to /cgi-bin/cstecgi.cgi with a JSON payload specifying topicurl=setWiFiEasyGuestCfg and attacker-controlled configuration parameters. No user interaction or authentication is required. The attack is limited to modifying guest Wi-Fi configuration, so integrity is affected while confidentiality and availability remain intact. Technical details are documented in the Notion Configuration Guide and VulDB #304842.
No verified exploit code is included here. See the referenced advisories for reproduction steps.
Detection Methods for CVE-2025-3664
Indicators of Compromise
- Unexpected HTTP POST requests to /cgi-bin/cstecgi.cgi containing topicurl=setWiFiEasyGuestCfg from unauthorized source addresses.
- Unexplained changes to the guest Wi-Fi SSID, passphrase, or broadcast state in the router configuration.
- Requests to the CGI endpoint originating from WAN-side IP addresses when remote management should be disabled.
Detection Strategies
- Inspect router HTTP access logs for POST requests targeting cstecgi.cgi with setWiFiEasyGuestCfg in the request body.
- Baseline guest Wi-Fi configuration and alert on out-of-band modifications not initiated through legitimate administrative sessions.
- Deploy network intrusion detection signatures that match the CGI request pattern combined with unauthenticated sessions.
Monitoring Recommendations
- Forward router syslog and web administration logs to a centralized logging platform for correlation.
- Monitor for successive set*Cfg requests originating from the same source, which may indicate broader configuration abuse.
- Track DHCP and wireless association events on guest networks for anomalous client activity following configuration changes.
How to Mitigate CVE-2025-3664
Immediate Actions Required
- Disable remote WAN-side management on affected TOTOLINK A3700R devices to limit exposure of cstecgi.cgi to the internet.
- Restrict LAN access to the router administration interface using firewall rules or a management VLAN.
- Change administrative credentials and audit current guest Wi-Fi configuration for unauthorized modification.
Patch Information
No vendor patch is available. According to the disclosure, the vendor was contacted but did not respond. Organizations should monitor the TOTOLINK Official Website for future firmware releases addressing this issue and consider replacing end-of-support hardware.
Workarounds
- Place affected routers behind a network segment that blocks untrusted access to the management HTTP interface.
- Disable the guest Wi-Fi feature if it is not required, reducing the impact of unauthorized configuration changes.
- Replace the affected TOTOLINK A3700R with a vendor-supported device that receives active security updates.
# Example: restrict access to the router management interface on an upstream firewall
iptables -A FORWARD -p tcp --dport 80 -d <router_ip> -s <admin_subnet> -j ACCEPT
iptables -A FORWARD -p tcp --dport 80 -d <router_ip> -j DROP
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
