CVE-2025-66954: Buffalo LinkStation Info Disclosure Flaw

CVE-2025-66954 Overview

A vulnerability exists in the Buffalo Link Station version 1.85-0.01 that allows unauthenticated or guest-level users to enumerate valid usernames and their associated privilege roles. The issue is triggered by modifying a parameter within requests sent to the /nasapi endpoint. This Information Exposure vulnerability (CWE-639: Authorization Bypass Through User-Controlled Key) enables attackers to gather intelligence about the system's user accounts without proper authentication.

Critical Impact

Attackers can enumerate valid usernames and their privilege levels on affected Buffalo Link Station devices, potentially enabling targeted credential attacks or privilege escalation attempts.

Affected Products

• Buffalo Link Station version 1.85-0.01

Discovery Timeline

• 2026-04-20 - CVE CVE-2025-66954 published to NVD
• 2026-04-20 - Last updated in NVD database

Technical Details for CVE-2025-66954

Vulnerability Analysis

This vulnerability falls under CWE-639 (Authorization Bypass Through User-Controlled Key), which occurs when the application uses user-controllable key values to determine which resources or functions are authorized. In this case, the Buffalo Link Station's /nasapi endpoint fails to properly validate authorization before returning sensitive user account information.

The attack can be performed remotely over the network and requires low privileges to execute. While no user interaction is required, the attacker needs at least guest-level access to the device. The vulnerability results in high confidentiality impact as it exposes usernames and their associated privilege roles, though it does not directly affect system integrity or availability.

Root Cause

The root cause stems from improper access control implementation in the /nasapi endpoint. The endpoint fails to verify that the requesting user has appropriate permissions to access user enumeration functionality. By manipulating request parameters, an attacker with minimal access rights can bypass authorization checks and retrieve information about other user accounts on the system, including their privilege levels.

Attack Vector

The attack is network-based and targets the /nasapi endpoint on vulnerable Buffalo Link Station devices. An attacker with guest-level or unauthenticated access modifies specific parameters in API requests to trigger the enumeration functionality. The response returns valid usernames and their associated privilege roles, providing valuable reconnaissance data for subsequent attacks.

The vulnerability could be exploited by:

1. Gaining guest-level access to the Buffalo Link Station
2. Sending crafted requests to the /nasapi endpoint with modified parameters
3. Parsing the response to extract valid usernames and privilege information
4. Using this information to target specific high-privilege accounts for credential attacks

For technical details and proof-of-concept information, refer to the GitHub PoC Repository.

Detection Methods for CVE-2025-66954

Indicators of Compromise

• Unusual or repeated requests to the /nasapi endpoint from unauthenticated or guest-level sessions
• API requests with modified or anomalous parameter values targeting user enumeration
• Increased volume of authentication attempts against enumerated usernames following reconnaissance activity

Detection Strategies

• Monitor web server logs for suspicious patterns of requests to the /nasapi endpoint
• Implement rate limiting and anomaly detection for API endpoints
• Review access logs for guest-level accounts making repeated API requests
• Deploy web application firewall (WAF) rules to detect parameter manipulation attempts

Monitoring Recommendations

• Enable verbose logging on the Buffalo Link Station device for API access
• Configure SIEM alerts for unusual patterns of /nasapi endpoint access
• Monitor for brute-force login attempts that may follow successful username enumeration
• Regularly audit user accounts and access logs for signs of unauthorized enumeration

How to Mitigate CVE-2025-66954

Immediate Actions Required

• Restrict network access to affected Buffalo Link Station devices to trusted networks only
• Disable guest account access if not required for business operations
• Implement network segmentation to isolate NAS devices from untrusted network segments
• Monitor for exploitation attempts while awaiting vendor patches

Patch Information

No vendor advisory or official patch information is currently available for this vulnerability. Monitor Buffalo's security advisories for future updates. Technical details are available in the GitHub PoC Repository.

Workarounds

• Place the Buffalo Link Station behind a firewall and restrict access to authorized IP addresses only
• Disable guest or anonymous access to minimize attack surface
• Implement VPN access requirements for remote administration
• Consider deploying a reverse proxy with additional authentication controls in front of the device

# Network access restriction example (firewall rule)
# Restrict access to NAS device to specific trusted subnet
iptables -A INPUT -s 192.168.1.0/24 -d <NAS_IP> -p tcp --dport 80 -j ACCEPT
iptables -A INPUT -s 192.168.1.0/24 -d <NAS_IP> -p tcp --dport 443 -j ACCEPT
iptables -A INPUT -d <NAS_IP> -p tcp --dport 80 -j DROP
iptables -A INPUT -d <NAS_IP> -p tcp --dport 443 -j DROP