CVE-2025-11625: WolfSSH Auth Bypass Vulnerability

CVE-2025-11625 Overview

CVE-2025-11625 is an improper host authentication vulnerability affecting wolfSSH version 1.4.20 and earlier clients. This authentication bypass flaw allows attackers to circumvent host authentication mechanisms and leak client credentials, potentially compromising secure communications and enabling man-in-the-middle attacks against SSH sessions.

Critical Impact

This vulnerability enables authentication bypass and credential leakage in wolfSSH clients, allowing attackers to intercept or hijack SSH sessions and steal sensitive authentication data.

Affected Products

• wolfSSH version 1.4.20 and earlier
• Applications and embedded systems using vulnerable wolfSSH client libraries
• IoT devices and embedded platforms relying on wolfSSH for secure communications

Discovery Timeline

• 2025-10-21 - CVE-2025-11625 published to NVD
• 2025-12-04 - Last updated in NVD database

Technical Details for CVE-2025-11625

Vulnerability Analysis

This vulnerability stems from improper host authentication implementation in the wolfSSH client library. The flaw is classified under CWE-287 (Improper Authentication), indicating a fundamental weakness in how the client validates the identity of SSH servers during the connection establishment phase.

When an SSH client connects to a server, it should verify the server's identity through cryptographic means—typically by validating the server's public key against known hosts or trusted certificates. The vulnerability in wolfSSH allows this critical verification step to be bypassed, enabling attackers to impersonate legitimate servers.

The network-based attack vector makes this vulnerability particularly dangerous in environments where clients connect to SSH servers over untrusted networks. An attacker positioned to intercept network traffic could present a malicious server that appears legitimate to the vulnerable client, capturing credentials and sensitive session data.

Root Cause

The root cause lies in improper host authentication validation within the wolfSSH client implementation. The client fails to adequately verify the server's identity during SSH handshake negotiations, allowing a malicious server to be accepted without proper cryptographic validation. This authentication weakness enables credential disclosure to unauthorized parties.

Attack Vector

An attacker can exploit this vulnerability through a network-based man-in-the-middle attack scenario. The attacker intercepts the connection between a vulnerable wolfSSH client and its intended server, presenting a rogue SSH server that the client incorrectly authenticates as legitimate.

The attack proceeds as follows: when a vulnerable client initiates an SSH connection, the attacker intercepts this connection and responds as the intended server. Due to the improper host authentication, the client accepts the attacker's server as legitimate. The client then transmits its authentication credentials—which may include passwords, private keys, or other sensitive authentication data—to the attacker's server instead of the intended destination.

This vulnerability requires user interaction in that the user must initiate an SSH connection, but requires no privileges on the attacker's part to exploit. The referenced GitHub Pull Request #840 provides additional technical details on the specific implementation flaw and its remediation.

Detection Methods for CVE-2025-11625

Indicators of Compromise

• Unexpected SSH connection failures or certificate warnings when connecting to known servers
• Evidence of man-in-the-middle attacks in network traffic logs showing altered server key fingerprints
• Authentication attempts logged from unexpected source IP addresses on SSH servers
• Client-side logs showing accepted server keys that don't match expected fingerprints

Detection Strategies

• Monitor for SSH connections where the server key fingerprint changes unexpectedly
• Implement network monitoring to detect potential MITM positioning attacks targeting SSH traffic
• Review wolfSSH client application logs for authentication anomalies or unexpected server responses
• Deploy intrusion detection signatures to identify exploitation attempts against SSH handshake sequences

Monitoring Recommendations

• Enable verbose logging on wolfSSH client applications to capture authentication events
• Implement centralized logging for all SSH client activity across the environment
• Monitor for credential reuse attempts that may indicate stolen authentication data
• Establish baseline SSH connection patterns to detect anomalous connection behavior

How to Mitigate CVE-2025-11625

Immediate Actions Required

• Identify all systems and applications using wolfSSH version 1.4.20 or earlier
• Upgrade to the patched version of wolfSSH as referenced in the official fix
• Review SSH server logs for signs of credential compromise or unauthorized access
• Consider rotating SSH credentials for clients that may have connected through untrusted networks

Patch Information

The wolfSSH development team has addressed this vulnerability through Pull Request #840 on GitHub. Organizations should upgrade to the latest version of wolfSSH that incorporates this fix. The patch corrects the improper host authentication logic, ensuring proper server identity verification during SSH connection establishment.

Workarounds

• Restrict wolfSSH client connections to trusted network segments where MITM attacks are less feasible
• Implement network-level protections such as VPNs or IPSec tunnels for SSH traffic over untrusted networks
• Use strict host key checking with pre-distributed known host files where possible
• Consider alternative SSH libraries until patching is complete in environments where immediate upgrade is not possible

# Verify wolfSSH version and check for vulnerable installations
# Review installed version
pkg info wolfssh 2>/dev/null || dpkg -l | grep wolfssh

# Check for applications linked against wolfSSH
ldd /path/to/application | grep wolfssh

# After upgrade, verify the new version is in use
wolfssh --version