CVE-2025-25609 Overview
CVE-2025-25609 is a buffer overflow vulnerability affecting the TOTOlink A3002R router running firmware version V1.1.1-B20200824.0128. The flaw resides in the formIpv6Setup interface handler within the /bin/boa web server binary. Improper input validation of the static_ipv6 parameter allows an authenticated attacker on an adjacent network to overflow a fixed-size buffer. Successful exploitation can lead to arbitrary code execution or a denial-of-service condition on the affected device. The vulnerability is classified under [CWE-120] (Classic Buffer Copy without Checking Size of Input).
Critical Impact
Attackers with low-privilege access on the local network can overflow buffers in the router's web server, compromising the confidentiality, integrity, and availability of the device.
Affected Products
- TOTOlink A3002R hardware appliance
- TOTOlink A3002R firmware version 1.1.1-B20200824.0128
- Deployments exposing the formIpv6Setup web interface on adjacent networks
Discovery Timeline
- 2025-02-28 - CVE-2025-25609 published to NVD
- 2026-06-17 - Last updated in NVD database
Technical Details for CVE-2025-25609
Vulnerability Analysis
The vulnerability exists in the /bin/boa HTTP server that handles administrative requests on the TOTOlink A3002R. When a user submits an IPv6 configuration through the formIpv6Setup endpoint, the handler reads the static_ipv6 parameter from the request without validating its length. The parameter is then copied into a fixed-size stack buffer using an unsafe string operation. An attacker can supply an oversized static_ipv6 value to overwrite adjacent stack memory, including saved return addresses. The attack requires low-privilege authentication and adjacent network access, meaning the attacker must be on the same Layer 2 network segment.
Root Cause
The root cause is missing bounds checking on the static_ipv6 request parameter within the formIpv6Setup handler. The boa binary trusts the length of user-supplied input and performs an unchecked copy into a stack buffer. This pattern matches [CWE-120] and reflects a broader lack of input validation across TOTOlink form handlers.
Attack Vector
Exploitation requires network adjacency and valid low-privilege credentials to the router's web administration interface. An attacker crafts an HTTP POST request to the formIpv6Setup endpoint containing an overlong static_ipv6 string. The oversized payload overflows the destination buffer during processing. Depending on payload construction, the attacker can crash the boa process or hijack execution flow to run arbitrary code with the privileges of the web server. Full technical reproduction steps are documented in the public firmcrosser advisory.
Detection Methods for CVE-2025-25609
Indicators of Compromise
- HTTP POST requests to /boafrm/formIpv6Setup containing abnormally long static_ipv6 parameter values
- Unexpected restarts, crashes, or unavailability of the boa web server process on the router
- New administrative sessions or configuration changes originating from adjacent network hosts
- Outbound connections from the router to unfamiliar external hosts following configuration requests
Detection Strategies
- Inspect HTTP traffic destined for the router's management interface and flag static_ipv6 values that exceed valid IPv6 address length
- Monitor router syslog output for repeated crashes or watchdog reboots of the boa process
- Compare running firmware versions against the vulnerable 1.1.1-B20200824.0128 build across the fleet
Monitoring Recommendations
- Log and alert on all authentication events and configuration changes on TOTOlink management interfaces
- Segment router management networks and monitor Layer 2 traffic for unauthorized hosts
- Capture packet traces of administrative sessions to retain evidence of malformed IPv6 configuration requests
How to Mitigate CVE-2025-25609
Immediate Actions Required
- Restrict access to the router's web administration interface to trusted management VLANs only
- Rotate administrative credentials and enforce strong, unique passwords on every affected device
- Disable IPv6 configuration features via the web interface where they are not operationally required
- Inventory all TOTOlink A3002R devices and confirm firmware versions against the vulnerable build
Patch Information
No vendor patch or fixed firmware version is referenced in the available advisory data for CVE-2025-25609. Administrators should monitor the TOTOlink support channels for an updated firmware release addressing the formIpv6Setup input validation flaw. Until a patch is available, apply the compensating controls listed below.
Workarounds
- Block external and untrusted internal access to the router's HTTP management port using upstream firewall rules
- Place vulnerable A3002R devices on an isolated management VLAN with strict access control lists
- Replace end-of-life or unsupported A3002R hardware with a currently supported router platform
- Disable remote administration and require console or LAN-only access for configuration changes
# Configuration example: restrict management access with an upstream firewall
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
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
