wolfSSL has announced the release of wolfSSH version 1.6.0, a significant update aimed at resolving five security vulnerabilities. Among these, a critical flaw was identified that allows potential man-in-the-middle (MITM) attacks by bypassing host key verification.
Details of the Security Flaws
Released on October 6, 2026, the wolfSSH 1.6.0 update targets several vulnerabilities. These include a privilege escalation issue on Windows, unauthorized key exchange abuses, unauthorized forwarding channels, and a memory corruption bug in the SFTP protocol.
The update classifies one vulnerability as critical, one as high severity, and three as medium. The critical issue, tracked as CVE-2026-16516, affects versions up to wolfSSH 1.5.0. It arises when the client’s key exchange does not verify if the server’s ECDSA curve aligns with the agreed algorithm, allowing attackers to exploit this mismatch.
Impact and Mitigation of Vulnerabilities
The potential exploit involves an attacker replacing the server’s host key with a different one that the client might accept due to weak public-key-checking procedures. This flaw does not imply automatic acceptance of malicious keys, as the application’s callback function plays a crucial role in verification. Researcher zhangph, also known as afldl on GitHub, is credited with discovering this issue.
The high-severity flaw, CVE-2026-83540, affects Windows-based wolfSSHd from versions 1.4.15 to 1.5.0. It involves shared authentication contexts potentially allowing unauthorized access to privileged accounts. This issue does not affect non-Windows builds.
CVE-2026-84897 highlights improper handling of Diffie-Hellman group exchange messages, where an attacker could force costly server-side operations by submitting chosen groups for verification. This flaw impacts versions 1.2.0 to 1.5.0.
Further Details and Recommendations
The remaining vulnerabilities include CVE-2026-81535, which affects versions 1.4.8 to 1.5.0 with forwarding enabled, and CVE-2026-83742, affecting non-Windows builds from versions 1.4.11 to 1.5.0. These involve unauthorized forwarding channel requests and SFTP path issues, respectively.
To mitigate these risks, wolfSSL advises users to upgrade to wolfSSH 1.6.0 promptly. The update includes enhancements such as stricter default key exchange protocols, RSA keys with a minimum of 2048 bits, and a capped number of failed authentication attempts.
Organizations should also review the release notes for detailed guidance on deployment and security improvements. This proactive measure ensures better protection against potential cyber threats.
