CVE-2023-48795: 9bis Kitty

Medium severity, CVSS 5.9. EPSS: 93.5% chance of exploitation in the next 30 days.

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 chacha20-poly1305@openssh.com and (if CBC is used) the -etm@openssh.com 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.

Affected products

9bis Kitty: up to and including 0.76.1.13
Apache Sshd: up to and including 2.11.0
Apache Sshj: up to and including 0.37.0
Apple macOS: from 14.0, before 14.4 (fixed in 14.4)
Asyncssh Project Asyncssh: before 2.14.2 (fixed in 2.14.2)
Bitvise SSH Client: before 9.33 (fixed in 9.33)
Bitvise SSH Server: before 9.32 (fixed in 9.32)
Connectbot Sshlib: before 2.2.22 (fixed in 2.2.22)
Crates Thrussh: before 0.35.1 (fixed in 0.35.1)
CrushFTP CrushFTP: up to and including 10.6.0; before 10.6.0 (fixed in 10.6.0)
Debian Debian Linux: version 10.0 only
Dropbear SSH Project Dropbear SSH: before 2022.83 (fixed in 2022.83)
Erlang Erlang/otp: before 22.3.4.27 (fixed in 22.3.4.27); from 23.0, before 23.3.4.20 (fixed in 23.3.4.20); from 24.0, before 24.3.4.15 (fixed in 24.3.4.15); from 25.0, before 25.3.2.8 (fixed in 25.3.2.8); from 26.0, before 26.2.1 (fixed in 26.2.1)
Fedoraproject Fedora: version 38 only; version 39 only
Filezilla-Project Filezilla Client: before 3.66.4 (fixed in 3.66.4)
Freebsd Freebsd: up to and including 12.4
Gentoo Security: affected versions not specified
Golang Crypto: before 0.17.0 (fixed in 0.17.0)
Jadaptive Maverick Synergy Java SSH API: before 3.1.0-snapshot (fixed in 3.1.0-snapshot)
Lancom-Systems Lanconfig: affected versions not specified
Lancom-Systems Lcos: up to and including 3.66.4
Lancom-Systems Lcos Fx: affected versions not specified
Lancom-Systems Lcos Lx: affected versions not specified
Lancom-Systems Lcos Sx: version 4.20 only; version 5.20 only
Libssh Libssh: before 0.10.6 (fixed in 0.10.6)
and 43 more

Published 2023-12-18. Last modified 2026-06-17.