CVE-2025-64053: Fanvil X210 Buffer Overflow Vulnerability

CVE-2025-64053 Overview

CVE-2025-64053 is a buffer overflow vulnerability affecting Fanvil X210 IP phones running firmware version 2.12.20. The flaw resides in the device web configuration interface, specifically the /cgi-bin/webconfig?page=upload&action=submit endpoint. Unauthenticated remote attackers can send a crafted POST request to trigger the overflow. Successful exploitation causes a denial of service and may allow execution of arbitrary commands on the device. The vulnerability is classified under CWE-120 — Buffer Copy without Checking Size of Input.

Critical Impact

Unauthenticated network attackers can crash Fanvil X210 phones or potentially execute arbitrary commands through a single crafted HTTP POST request.

Affected Products

• Fanvil X210 IP Phone hardware (version 2.0)
• Fanvil X210 firmware version 2.12.20
• Deployments exposing the device web configuration interface (/cgi-bin/webconfig)

Discovery Timeline

• 2025-12-05 - CVE-2025-64053 published to NVD
• 2026-01-09 - Last updated in NVD database

Technical Details for CVE-2025-64053

Vulnerability Analysis

The vulnerability exists in the CGI handler responsible for processing file upload requests on the Fanvil X210 web management interface. The handler reads attacker-controlled data from a POST request to /cgi-bin/webconfig?page=upload&action=submit without enforcing proper length validation. When the input exceeds the size of the destination buffer, adjacent memory is overwritten. This corruption causes the embedded web service to crash, producing a denial-of-service condition. Depending on memory layout and processor architecture, the overflow may also be leveraged to redirect execution and run arbitrary commands on the underlying firmware.

Root Cause

The root cause is a missing or insufficient bounds check on user-supplied input copied into a fixed-size stack or heap buffer within the webconfig CGI binary. Standard memory copy operations such as strcpy, sprintf, or memcpy with attacker-influenced length parameters allow data to extend beyond allocated memory. This pattern is characteristic of [CWE-120].

Attack Vector

The endpoint is accessible over the network, requires no authentication, and demands no user interaction. An attacker with network reachability to the phone's HTTP service issues a POST request containing an oversized payload to the upload endpoint. The CGI process parses the request, copies the oversized field into a smaller buffer, and corrupts memory. Refer to the GitHub Security Advisory for CVE-2025-64053 for the technical proof submitted by the reporter.

Detection Methods for CVE-2025-64053

Indicators of Compromise

• Unexpected crashes or reboots of Fanvil X210 phones, especially correlated with inbound HTTP traffic.
• HTTP POST requests to /cgi-bin/webconfig?page=upload&action=submit originating from untrusted networks or unusual source IPs.
• Abnormally large request bodies or oversized form fields targeting the webconfig CGI endpoint.

Detection Strategies

• Inspect web access logs from the device or upstream proxy for POST requests to the webconfig upload endpoint with content-length values exceeding normal upload sizes.
• Deploy network IDS signatures matching long parameter values directed at /cgi-bin/webconfig URIs on Fanvil device IP ranges.
• Monitor SNMP or syslog feeds from VoIP infrastructure for repeated process restarts on X210 endpoints.

Monitoring Recommendations

• Enable centralized syslog collection from Fanvil phones and alert on web service crashes.
• Track availability of VoIP endpoints and flag repeated registration loss as a possible exploitation symptom.
• Restrict and monitor management plane traffic between user VLANs and voice VLANs to detect unauthorized access attempts.

How to Mitigate CVE-2025-64053

Immediate Actions Required

• Restrict access to the X210 web management interface using ACLs so only trusted administrative hosts can reach /cgi-bin/webconfig.
• Place voice infrastructure on a dedicated VLAN isolated from general user and guest networks.
• Disable the HTTP management interface on devices that do not require remote configuration.

Patch Information

No vendor advisory or patched firmware version is referenced in the enriched CVE data at the time of writing. Administrators should consult the Fanvil Official Website and the GitHub Security Advisory for CVE-2025-64053 for updates and apply firmware newer than 2.12.20 once released.

Workarounds

• Block inbound traffic to TCP ports used by the device web interface from untrusted segments at the firewall.
• Enforce strong administrative credentials and disable any unused remote management protocols on the phone.
• Monitor for crash patterns and rate-limit HTTP requests to the device management interface where supported.

# Example: restrict access to Fanvil X210 web management interface to a trusted admin subnet
iptables -A FORWARD -p tcp -d <FANVIL_X210_IP> --dport 80 -s 10.10.0.0/24 -j ACCEPT
iptables -A FORWARD -p tcp -d <FANVIL_X210_IP> --dport 80 -j DROP
iptables -A FORWARD -p tcp -d <FANVIL_X210_IP> --dport 443 -s 10.10.0.0/24 -j ACCEPT
iptables -A FORWARD -p tcp -d <FANVIL_X210_IP> --dport 443 -j DROP