The credentials for the local user "user-app" may be exposed in log files, potentially enabling a low-privileged local attacker with access to the logs to authenticate via SSH as the limited user "user-app". Charging could be interrupted.

When writing data larger than 4GB in a single Write call on an SSH channel, an integer overflow in the internal payload size calculation caused the write loop to spin indefinitely, sending empty packets without making progress. The size comparison now uses int64 to prevent truncation.

SSH Tectia Server before 6.6.6 sometimes allows attackers to read and alter a user's session traffic.

PrivX before 34.0 allows data exfiltration and denial of service via the REST API. This is fixed in minor versions 33.1, 32.3, 31.3, and later, and in major version 34.0 and later,

Summary

Terrapin is a prefix truncation attack targeting the SSH protocol. More precisely, Terrapin breaks the integrity of SSH's secure channel. By carefully adjusting the sequence numbers during the handshake, an attacker can remove an arbitrary amount of messages sent by the client or server at the beginning of the secure channel without the client or server noticing it.

Mitigations

To mitigate this protocol vulnerability, OpenSSH suggested a so-called "strict kex" which alters the SSH handshake to ensure a Man-in-the-Middle attacker cannot introduce unauthenticated messages as well as convey sequence number manipulation across handshakes.

Warning: To take effect, both the client and server must support this countermeasure.

As a stop-gap measure, peers may also (temporarily) disable the affected algorithms and use unaffected alternatives like AES-GCM instead until patches are available.

Details

The SSH specifications of ChaCha20-Poly1305 (chacha20-poly1305@openssh.com) and Encrypt-then-MAC (-etm@openssh.com MACs) are vulnerable against an arbitrary prefix truncation attack (a.k.a. Terrapin attack). This allows for an extension negotiation downgrade by stripping the SSHMSGEXTINFO sent after the first message after SSHMSGNEWKEYS, downgrading security, and disabling attack countermeasures in some versions of OpenSSH. When targeting Encrypt-then-MAC, this attack requires the use of a CBC cipher to be practically exploitable due to the internal workings of the cipher mode. Additionally, this novel attack technique can be used to exploit previously unexploitable implementation flaws in a Man-in-the-Middle scenario.

The attack works by an attacker injecting an arbitrary number of SSHMSGIGNORE messages during the initial key exchange and consequently removing the same number of messages just after the initial key exchange has concluded. This is possible due to missing authentication of the excess SSHMSGIGNORE messages and the fact that the implicit sequence numbers used within the SSH protocol are only checked after the initial key exchange.

In the case of ChaCha20-Poly1305, the attack is guaranteed to work on every connection as this cipher does not maintain an internal state other than the message's sequence number. In the case of Encrypt-Then-MAC, practical exploitation requires the use of a CBC cipher; while theoretical integrity is broken for all ciphers when using this mode, message processing will fail at the application layer for CTR and stream ciphers.

For more details see https://terrapin-attack.com.

Impact

This attack targets the specification of ChaCha20-Poly1305 (chacha20-poly1305@openssh.com) and Encrypt-then-MAC (-etm@openssh.com), which are widely adopted by well-known SSH implementations and can be considered de-facto standard. These algorithms can be practically exploited; however, in the case of Encrypt-Then-MAC, we additionally require the use of a CBC cipher. As a consequence, this attack works against all well-behaving SSH implementations supporting either of those algorithms and can be used to downgrade (but not fully strip) connection security in case SSH extension negotiation (RFC8308) is supported. The attack may also enable attackers to exploit certain implementation flaws in a man-in-the-middle (MitM) scenario.

SSH Tectia Client and Server before 6.4.19 on Windows allow local privilege escalation. ConnectSecure on Windows is affected.

SSH Tectia Client and Server before 6.4.19 on Windows have weak key generation. ConnectSecure on Windows is affected.

SSH Tectia Client and Server before 6.4.19 on Windows allow local privilege escalation in nonstandard conditions. ConnectSecure on Windows is affected.

The SSH USERAUTH CHANGE REQUEST feature in SSH Tectia Server 6.0.4 through 6.0.20, 6.1.0 through 6.1.12, 6.2.0 through 6.2.5, and 6.3.0 through 6.3.2 on UNIX and Linux, when old-style password authentication is enabled, allows remote attackers to bypass authentication via a crafted session involving entry of blank passwords, as demonstrated by a root login session from a modified OpenSSH client with an added inputuserauthpasswdchangereq call in sshconnect2.c.

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.

Error handling in the SSH protocol in (1) SSH Tectia Client and Server and Connector 4.0 through 4.4.11, 5.0 through 5.2.4, and 5.3 through 5.3.8; Client and Server and ConnectSecure 6.0 through 6.0.4; Server for Linux on IBM System z 6.0.4; Server for IBM z/OS 5.5.1 and earlier, 6.0.0, and 6.0.1; and Client 4.0-J through 4.3.3-J and 4.0-K through 4.3.10-K; and (2) OpenSSH 4.7p1 and possibly other versions, when using a block cipher algorithm in Cipher Block Chaining (CBC) mode, makes it easier for remote attackers to recover certain plaintext data from an arbitrary block of ciphertext in an SSH session via unknown vectors.

ssh-signer in SSH Tectia Client and Server 5.x before 5.2.4, and 5.3.x before 5.3.6, on Unix and Linux allows local users to gain privileges via unspecified vectors.

SSH Tectia Server for IBM z/OS before 5.4.0 uses insecure world-writable permissions for (1) the server pid file, which allows local users to cause arbitrary processes to be stopped, or (2) when BPXBATCHUMASK is missing from the environment, creates HFS files with insecure permissions, which allows local users to read or modify these files and have other unknown impact.

SSH Tectia Client/Server/Connector 5.1.0 and earlier, Manager 2.2.0 and earlier, and other products, when using an RSA key with exponent 3, removes PKCS-1 padding before generating a hash, which allows remote attackers to forge a PKCS #1 v1.5 signature that is signed by that RSA key and prevents Tectia from correctly verifying X.509 and other certificates that use PKCS #1, a similar issue to CVE-2006-4339.

Unquoted Windows search path vulnerability in multiple SSH Tectia products, including Client/Server/Connector 5.0.0 and 5.0.1 and Client/Server before 4.4.5, and Manager 2.12 and earlier, when running on Windows, might allow local users to gain privileges via a malicious program file under "Program Files" or its subdirectories.

SSH Tectia Management Agent 2.1.2 allows local users to gain root privileges by running a program called sshd, which is obtained from a process listing when the "Restart" action is selected from the Management server GUI, which causes the agent to locate the pathname of the user's program and restart it with root privileges.

SSH Tectia Server 5.0.0 (A, F, and T), when allowing host-based authentication only, allows users to log in with the wrong credentials.

SSH Tectia Server 4.3.1 and earlier, and SSH Secure Shell for Windows Servers, uses insecure permissions when generating the Secure Shell host identification key, which allows local users to access the key and spoof the server.

SSH Secure Shell before 3.2.9 allows remote attackers to cause a denial of service via malformed BER/DER packets.

Race condition in SSH Tectia Server 4.0.3 and 4.0.4 for Unix, when the password change plugin (ssh-passwd-plugin) is enabled, allows local users to obtain the server's private key.

SSH Secure Shell for Servers 3.0.0 to 3.1.1 allows remote attackers to override the AllowedAuthentications configuration and use less secure authentication schemes (e.g. password) than configured for the server.

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.

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 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.

SSH Secure Shell 3.0.0 on Unix systems does not properly perform password authentication to the sshd2 daemon, which allows local users to gain access to accounts with short password fields, such as locked accounts that use "NP" in the password field.

The SSH protocols 1 and 2 (aka SSH-2) as implemented in OpenSSH and other packages have various weaknesses which can allow a remote attacker to obtain the following information via sniffing: (1) password lengths or ranges of lengths, which simplifies brute force password guessing, (2) whether RSA or DSA authentication is being used, (3) the number of authorizedkeys in RSA authentication, or (4) the lengths of shell commands.

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.

SSH Communications Security sshd 2.4 for Windows allows remote attackers to create a denial of service via a large number of simultaneous connections.

SSH daemon version 1 (aka SSHD-1 or SSH-1) 1.2.30 and earlier does not log repeated login attempts, which could allow remote attackers to compromise accounts without detection via a brute force attack.

ssh-keygen in ssh 1.2.27 - 1.2.30 with Secure-RPC can allow local attackers to recover a SUN-DES-1 magic phrase generated by another user, which the attacker can use to decrypt that user's private key file.