CVE-2025-41251: VMware NSX Auth Bypass Vulnerability

CVE-2025-41251 Overview

CVE-2025-41251 is a weak password recovery mechanism vulnerability affecting VMware NSX, a widely deployed network virtualization and security platform. This vulnerability allows unauthenticated malicious actors to enumerate valid usernames through the password recovery mechanism, which can serve as a precursor to brute-force credential attacks against the affected systems.

The vulnerability stems from improper handling of password recovery requests (CWE-640: Weak Password Recovery Mechanism for Forgotten Password), where the system provides distinguishable responses that reveal whether a username exists in the system. This information disclosure enables attackers to compile lists of valid user accounts for subsequent credential stuffing or password spraying attacks.

Critical Impact

Unauthenticated remote attackers can enumerate valid usernames, enabling targeted brute-force attacks against VMware NSX infrastructure. This is particularly concerning given NSX's role in managing network security policies across virtualized environments.

Affected Products

• VMware NSX versions 9.x.x.x, 4.2.x, 4.1.x, 4.0.x
• NSX-T 3.x
• VMware Cloud Foundation (with NSX) versions 5.x, 4.5.x

Discovery Timeline

• Reported by - National Security Agency (NSA)
• 2025-09-29 - CVE-2025-41251 published to NVD
• 2025-09-29 - Last updated in NVD database

Technical Details for CVE-2025-41251

Vulnerability Analysis

This vulnerability exists in VMware NSX's password recovery functionality. The weakness allows remote, unauthenticated attackers to determine whether specific usernames exist within the system by analyzing responses from the password recovery endpoint. When a valid username is submitted, the system returns a different response compared to when an invalid username is provided, creating an oracle that attackers can exploit.

The impact of username enumeration extends beyond simple information disclosure. Once attackers compile a list of valid accounts, they can conduct targeted password attacks with significantly higher efficiency. In enterprise environments where NSX manages network microsegmentation and security policies, compromised credentials could lead to unauthorized access to critical network infrastructure controls.

Root Cause

The root cause is classified under CWE-640: Weak Password Recovery Mechanism for Forgotten Password. The password recovery functionality fails to provide uniform responses regardless of whether the submitted username exists in the system. This design flaw violates the security principle of providing identical responses for both valid and invalid account recovery attempts to prevent enumeration attacks.

Attack Vector

The attack can be executed remotely over the network without requiring any prior authentication. An attacker interacts with the password recovery mechanism by submitting username guesses and observing the system's responses. Variations in response content, timing, or HTTP status codes can indicate whether a username is valid.

The attack methodology typically involves:

1. Identifying the password recovery endpoint on the VMware NSX management interface
2. Submitting a series of username guesses (potentially using wordlists of common usernames or harvested names)
3. Analyzing response differentials to identify valid accounts
4. Compiling enumerated usernames for subsequent brute-force or credential stuffing attacks

This vulnerability has been rated as "Important" by the vendor with no workarounds available, emphasizing the necessity of applying patches promptly.

Detection Methods for CVE-2025-41251

Indicators of Compromise

• Unusual volume of password recovery requests from single or distributed source IPs
• Sequential or automated requests to the password recovery endpoint with varying usernames
• Authentication failures targeting multiple user accounts that were not previously attempted
• Evidence of credential stuffing attacks following periods of unusual password recovery activity

Detection Strategies

• Monitor web server logs for abnormal patterns of requests to password recovery endpoints
• Implement rate limiting detection rules that alert on excessive password recovery attempts
• Deploy web application firewall (WAF) rules to detect and block automated enumeration attempts
• Correlate password recovery request patterns with subsequent authentication attempt patterns

Monitoring Recommendations

• Enable detailed logging on VMware NSX management interfaces, particularly for authentication-related endpoints
• Configure SIEM rules to detect statistical anomalies in password recovery request volumes
• Establish baseline metrics for normal password recovery usage to facilitate anomaly detection
• Monitor for reconnaissance patterns that may indicate pre-attack username harvesting activities

How to Mitigate CVE-2025-41251

Immediate Actions Required

• Upgrade VMware NSX to the fixed versions as specified by Broadcom immediately
• Implement network-level access controls to restrict access to NSX management interfaces
• Deploy rate limiting on password recovery endpoints as a temporary measure
• Review authentication logs for signs of username enumeration attempts

Patch Information

VMware (Broadcom) has released security patches addressing this vulnerability. Organizations should upgrade to the following fixed versions:

For detailed patch information and download links, refer to the Broadcom Security Advisory #36150.

Workarounds

• No vendor-provided workarounds are available for this vulnerability
• Organizations must apply the security patches to fully remediate the issue
• Restrict network access to NSX management interfaces to trusted networks only as a compensating control
• Consider implementing additional authentication layers (such as VPN or jump hosts) for management access

# Example: Restrict management interface access via firewall rules
# This is a compensating control - patching is still required

# Allow management access only from trusted admin network
iptables -A INPUT -p tcp --dport 443 -s 10.0.100.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -j DROP

# Enable logging for blocked access attempts
iptables -A INPUT -p tcp --dport 443 -j LOG --log-prefix "NSX-MGMT-BLOCKED: "