CVE-2026-59851

Versions of libssh before 0.6.5 have a state validation issue in the handling of SSH_MSG_NEWKEYS and SSH_MSG_KEXDH_REPLY packets, which can lead to system crashes.

In the libssh library, if data packets are processed after a channel is closed, channel data callbacks can be invoked after the associated data has already been freed, leading to crashes or possible use-after-free conditions.

A logic error in libssh's automatic certificate-based public key authentication causes libssh clients to loop indefinitely when configured certificates are missing or repeatedly rejected by a server, leading to denial of service.

Vulnerability in libssh. A malicious SFTP server can send responses for unknown request IDs, causing unbounded memory growth and client-side denial of service.

A flaw in libssh. Incorrect AES-GCM finalization checks in builds using the OpenSSL backend can effectively remove integrity protection, allowing an in-path attacker to modify plaintext on the wire without detection.

A flaw in libssh: a malicious username expanded through %r in ProxyCommand handling can inject shell metacharacters, exposing environment variables and causing unintended shell behavior.

In libssh, when ProxyCommand is used, an unchecked fork() failure can result in storing PID -1. During cleanup, signals may be sent to processes in the caller's process tree, causing local denial of service.

A flaw in libssh: a remote authenticated client can issue SFTP_READ requests with an arbitrarily large length, causing the SFTP server to allocate excessive memory and potentially exhaust it.

A flaw in libssh: a remote authenticated peer can advertise a zero maximum packet size in SSH_MSG_CHANNEL_OPEN, causing infinite channel write loops and CPU exhaustion.

In libssh, during server-side GSSAPI key exchange, a short Curve25519 public key is copied without proper length validation, causing an out-of-bounds heap read.