Terrapin attack allows to downgrade SSH protocol security
Vulnerabilities mentionedAll →
| CVE | Vulnerability | CVSS | EPSS | Flags | Affected | Exposure | Published |
|---|---|---|---|---|---|---|---|
| CVE-2023-48795 | The SSH transport protocol with certain OpenSSH extensions, found in OpenSSH before 9.6 and other products, allows remote attackers to bypass integrity checks s The SSH transport protocol with certain OpenSSH extensions, found in OpenSSH before 9.6 and other products, allows remote attackers to bypass integrity checks such that some packets are omitted (from the extension negotiation message), and a client and server may consequently end up with a connection for which some security features have been downgraded or disabled, aka a Terrapin attack. This occurs because the SSH Binary Packet Protocol (BPP), implemented by these extensions, mishandles the handshake phase and mishandles use of sequence numbers. For example, there is an effective attack against SSH's use of ChaCha20-Poly1305 (and CBC with Encrypt-then-MAC). The bypass occurs in [email protected] and (if CBC is used) the [email protected] MAC algorithms. This also affects Maverick Synergy Java SSH API before 3.1.0-SNAPSHOT, Dropbear through 2022.83, Ssh before 5.1.1 in Erlang/OTP, PuTTY before 0.80, AsyncSSH before 2.14.2, golang.org/x/crypto before 0.17.0, libssh before 0.10.6, libssh2 through 1.11.0, Thorn Tech SFTP Gateway before 3.4.6, Tera Term before 5.1, Paramiko before 3.4.0, jsch before 0.2.15, SFTPGo before 2.5.6, Netgate pfSense Plus through 23.09.1, Netgate pfSense CE through 2.7.2, HPN-SSH through 18.2.0, ProFTPD before 1.3.8b (and before 1.3.9rc2), ORYX CycloneSSH before 2.3.4, NetSarang XShell 7 before Build 0144, CrushFTP before 10.6.0, ConnectBot SSH library before 2.2.22, Apache MINA sshd through 2.11.0, sshj through 0.37.0, TinySSH through 20230101, trilead-ssh2 6401, LANCOM LCOS and LANconfig, FileZilla before 3.66.4, Nova before 11.8, PKIX-SSH before 14.4, SecureCRT before 9.4.3, Transmit5 before 5.10.4, Win32-OpenSSH before 9.5.0.0p1-Beta, WinSCP before 6.2.2, Bitvise SSH Server before 9.32, Bitvise SSH Client before 9.33, KiTTY through 0.76.1.13, the net-ssh gem 7.2.0 for Ruby, the mscdex ssh2 module before 1.15.0 for Node.js, the thrussh library before 0.35.1 for Rust, and the Russh crate before 0.40.2 for Rust. NVD description · AI analysis pending | 5.9 | 93% |
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Full article419 words · extracted from securityaffairs.com · click to collapse
Researchers discovered an SSH vulnerability, called Terrapin, that could allow an attacker to downgrade the connection’s security.
Security researchers from Ruhr University Bochum (Fabian Bäumer, Marcus Brinkmann, Jörg Schwenk) discovered a vulnerability, called Terrapin (CVE-2023-48795, CVSS score 5.9), in the Secure Shell (SSH) cryptographic network protocol. An attacker can trigger the flaw to downgrade the connection’s security implemented by the protocol.
The Secure Shell Protocol (SSH) is a cryptographic network protocol for operating network services securely over an unsecured network. Its most notable applications are remote login and command-line execution.
Terrapin is a prefix truncation attack, it works by breaking 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.” reads the advisory published by the researchers. “The attack can be performed in practice, allowing an attacker to downgrade the connection’s security by truncating the extension negotiation message (RFC8308) from the transcript. The truncation can lead to using less secure client authentication algorithms and deactivating specific countermeasures against keystroke timing attacks in OpenSSH 9.5.”
The truncation may result in the utilization of less secure client authentication algorithms and the deactivation of specific countermeasures against keystroke timing attacks in OpenSSH 9.5.
To perform the Terrapin attack, a threat actor must be able to perform a MitM attack at the network layer. Another pre-requirement is that the connection must be secured by either ChaCha20-Poly1305 or CBC with Encrypt-then-MAC.
The Terrapin attack could allow to intercept sensitive data or take over critical systems using administrator privileged access.
The following image shows the Terrapin attack.
“The attacker can drop the EXT_INFO message, used for negotiating several protocol extensions, without the client or server noticing it. Usually, packet deletion would be detected by the client when receiving the next binary packet sent by the server, as sequence numbers would mismatch.” continues the analysis. “To avoid this, an attacker injects an ignored packet during the handshake to offset the sequence numbers accordingly.”
The researchers published a full technical paper titled “Terrapin Attack: Breaking SSH Channel Integrity By Sequence Number Manipulation.”
The experts also published a simple console application on GitHub written in Go that can allow to determine whether an SSH server or client is vulnerable to the Terrapin attack.
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