CVE-2025-14942 Overview
A critical authentication bypass vulnerability has been discovered in wolfSSH's key exchange state machine that allows attackers to manipulate the SSH handshake process. This flaw enables multiple attack scenarios including leaking client passwords in cleartext, tricking clients into sending bogus signatures, or completely bypassing user authentication. The vulnerability affects wolfSSH version 1.4.21 and earlier, impacting both client and server applications using this library.
Critical Impact
Attackers can intercept SSH sessions to steal credentials in plaintext, forge authentication signatures, or bypass user authentication entirely, compromising the confidentiality and integrity of encrypted communications.
Affected Products
- wolfSSH version 1.4.21 and earlier (client applications)
- wolfSSH version 1.4.21 and earlier (server applications)
- Applications built using vulnerable wolfSSH library versions
Discovery Timeline
- 2026-01-06 - CVE CVE-2025-14942 published to NVD
- 2026-01-08 - Last updated in NVD database
Technical Details for CVE-2025-14942
Vulnerability Analysis
This vulnerability stems from improper authentication handling (CWE-287) in wolfSSH's key exchange state machine implementation. The SSH protocol relies on a carefully orchestrated state machine to handle the key exchange and authentication phases securely. In affected versions of wolfSSH, the state machine can be manipulated by an attacker positioned between the client and server, enabling man-in-the-middle attacks.
The flaw allows three distinct attack scenarios: First, an attacker can force the client to transmit its password in cleartext by manipulating the negotiation process. Second, the state machine can be exploited to trick the client into generating and sending an invalid or bogus cryptographic signature. Third, and most critically, an attacker can manipulate the state transitions to cause the client to skip the user authentication phase entirely.
Root Cause
The vulnerability exists due to improper state validation in the key exchange state machine. The implementation fails to properly enforce the expected sequence of SSH protocol messages, allowing an attacker to inject or modify messages that alter the state machine's behavior. This represents a fundamental flaw in the protocol implementation where state transitions are not adequately validated against expected protocol behavior.
Attack Vector
The attack requires network access and targets the SSH connection establishment process. An attacker capable of intercepting network traffic between a wolfSSH client and server can manipulate the key exchange messages to exploit the state machine flaw. The attack requires some user interaction in the form of the victim initiating an SSH connection.
The exploitation involves injecting or modifying SSH protocol messages during the initial handshake to manipulate the state machine into an unintended state. This could involve:
- Modifying negotiation messages to force fallback to insecure authentication methods
- Injecting messages that cause state machine transitions that skip security checks
- Manipulating the sequence of protocol messages to expose credentials before encryption is established
Detection Methods for CVE-2025-14942
Indicators of Compromise
- Unexpected or malformed SSH protocol messages during connection establishment
- Authentication attempts that succeed without proper credential validation
- Cleartext password transmissions detected in SSH session traffic
- Anomalous state transitions in SSH handshake logging
Detection Strategies
- Monitor network traffic for SSH connections exhibiting unusual handshake patterns
- Implement deep packet inspection to identify malformed or out-of-sequence SSH protocol messages
- Review authentication logs for connections that bypass expected authentication steps
- Deploy network intrusion detection rules targeting SSH protocol anomalies
Monitoring Recommendations
- Enable verbose logging on wolfSSH applications to capture detailed handshake information
- Implement network-level monitoring for SSH traffic anomalies between known clients and servers
- Set up alerts for successful authentications that lack corresponding credential validation events
- Monitor for unusual patterns in SSH key exchange timing or message ordering
How to Mitigate CVE-2025-14942
Immediate Actions Required
- Update wolfSSH to a version that includes the security fix (versions after 1.4.21)
- Apply the security patch available via GitHub Pull Request #855
- Rotate and update all credentials used with affected wolfSSH applications
- Review authentication logs for signs of previous exploitation
Patch Information
The fix for this vulnerability is available through the official wolfSSH repository. Users should apply the patch from GitHub Pull Request #855 or update to a patched version of wolfSSH. The security researchers Aina Toky Rasoamanana of Valeo and Olivier Levillain of Telecom SudParis who discovered this vulnerability have been acknowledged by the vendor.
Server applications using wolfSSH should also be updated, as the same defect exists in the server-side implementation even though specific server attacks have not been identified.
Workarounds
- Restrict SSH connections to trusted network segments where man-in-the-middle attacks are less feasible
- Implement additional network-layer authentication such as VPNs or IPsec tunnels for wolfSSH connections
- Consider temporarily using alternative SSH implementations until the patch can be applied
- Implement network monitoring to detect and alert on suspicious SSH traffic patterns
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
