The SSH-1 protocol allows remote servers to conduct man-in-the-middle attacks and replay a client challenge response to a target server by creating a Session ID that matches the Session ID of the target, but which uses a public key pair that is weaker than the target's public key, which allows the attacker to compute the corresponding private key and use the target's Session ID with the compromised key pair to masquerade as the target.

SSH before 2.0 disables host key checking when connecting to the localhost, which allows remote attackers to silently redirect connections to the localhost by poisoning the client's DNS cache.

SSH before 2.0, when using RC4 and password authentication, allows remote attackers to replay messages until a new server key (VK) is generated.

SSH before 2.0, with RC4 encryption and the "disallow NULL passwords" option enabled, makes it easier for remote attackers to guess portions of user passwords by replaying user sessions with certain modifications, which trigger different messages depending on whether the guess is correct or not.

SSH Secure Shell for Servers and SSH Secure Shell for Workstations 2.0.13 through 3.2.1, when running without a PTY, does not call setsid to remove the child process from the process group of the parent process, which allows attackers to gain certain privileges.

Buffer overflow in the URL catcher feature for SSH Secure Shell for Workstations client 3.1 to 3.2.0 allows remote attackers to execute arbitrary code via a long URL.

SSH 1 through 3, and possibly other versions, allows local users to bypass restricted shells such as rbash or rksh by uploading a script to a world-writeable directory, then executing that script to gain normal shell access.

Implementations of SSH version 1.5, including (1) OpenSSH up to version 2.3.0, (2) AppGate, and (3) ssh-1 up to version 1.2.31, in certain configurations, allow a remote attacker to decrypt and/or alter traffic via a "Bleichenbacher attack" on PKCS#1 version 1.5.

The random number generator in the Crypto application before 2.0.2.2, and SSH before 2.0.5, as used in the Erlang/OTP ssh library before R14B03, uses predictable seeds based on the current time, which makes it easier for remote attackers to guess DSA host and SSH session keys.