GHSA-45x7-px36-x8w8: Medium severity go/golang.org/x/crypto vulnerability
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.
Other sources
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.
— OSV
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
go/golang.org/x/cryptoto a version that resolves this vulnerability.Fixed in 0.0.0-20231218163308-9d2ee975ef9f - Upgrade
Upgrade
go/golang.org/x/cryptoto a version that resolves this vulnerability.Fixed in 0.17.0 - Upgrade
Upgrade
pip/paramikoto a version that resolves this vulnerability.Fixed in 3.4.0 - Upgrade
Upgrade
rust/russhto a version that resolves this vulnerability.Fixed in 0.40.2 - Upgrade
Upgrade
OpenSSHto a version that resolves this vulnerability.Fixed in 9.6 - Upgrade
Upgrade
Maverick Synergy Java SSH APIto a version that resolves this vulnerability.Fixed in 3.1.0-SNAPSHOT - Upgrade
Upgrade
Ssh in Erlang/OTPto a version that resolves this vulnerability.Fixed in 5.1.1 - Upgrade
Upgrade
PuTTYto a version that resolves this vulnerability.Fixed in 0.80 - Upgrade
Upgrade
AsyncSSHto a version that resolves this vulnerability.Fixed in 2.14.2 - Upgrade
Upgrade
golang.org/x/cryptoto a version that resolves this vulnerability.Fixed in 0.17.0 - Upgrade
Upgrade
libsshto a version that resolves this vulnerability.Fixed in 0.10.6 - Upgrade
Upgrade
Thorn Tech SFTP Gatewayto a version that resolves this vulnerability.Fixed in 3.4.6 - Upgrade
Upgrade
Tera Termto a version that resolves this vulnerability.Fixed in 5.1 - Upgrade
Upgrade
Paramikoto a version that resolves this vulnerability.Fixed in 3.4.0 - Upgrade
Upgrade
jschto a version that resolves this vulnerability.Fixed in 0.2.15 - Upgrade
Upgrade
SFTPGoto a version that resolves this vulnerability.Fixed in 2.5.6 - Upgrade
Upgrade
ORYX CycloneSSHto a version that resolves this vulnerability.Fixed in 2.3.4 - Upgrade
Upgrade
NetSarang XShell 7to a version that resolves this vulnerability.Fixed in Build 0144 - Upgrade
Upgrade
CrushFTPto a version that resolves this vulnerability.Fixed in 10.6.0 - Upgrade
Upgrade
ConnectBot SSH libraryto a version that resolves this vulnerability.Fixed in 2.2.22 - Upgrade
Upgrade
ProFTPDto a version that resolves this vulnerability.Fixed in 1.3.8b - Upgrade
Upgrade
FileZillato a version that resolves this vulnerability.Fixed in 3.66.4 - Upgrade
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Novato a version that resolves this vulnerability.Fixed in 11.8 - Upgrade
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PKIX-SSHto a version that resolves this vulnerability.Fixed in 14.4 - Upgrade
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SecureCRTto a version that resolves this vulnerability.Fixed in 9.4.3 - Upgrade
Upgrade
Transmit5to a version that resolves this vulnerability.Fixed in 5.10.4 - Upgrade
Upgrade
Win32-OpenSSHto a version that resolves this vulnerability.Fixed in 9.5.0.0p1-Beta - Upgrade
Upgrade
WinSCPto a version that resolves this vulnerability.Fixed in 6.2.2 - Upgrade
Upgrade
Bitvise SSH Serverto a version that resolves this vulnerability.Fixed in 9.32 - Upgrade
Upgrade
Bitvise SSH Clientto a version that resolves this vulnerability.Fixed in 9.33 - Upgrade
Upgrade
the mscdex ssh2 module for Node.jsto a version that resolves this vulnerability.Fixed in 1.15.0 - Upgrade
Upgrade
thrussh library for Rustto a version that resolves this vulnerability.Fixed in 0.35.1 - Upgrade
Upgrade
Russh crate for Rustto a version that resolves this vulnerability.Fixed in 0.40.2 - Configuration
Temporarily disable chacha20-poly1305@openssh.com and *-etm@openssh.com, using unaffected alternatives such as AES-GCM until patches are available.
SSH ChaCha20-Poly1305 and Encrypt-then-MAC algorithms = disabled; use AES-GCM instead - Configuration
Enable the strict kex countermeasure on both the client and server where supported.
SSH client and server strict kex = enabled
Event History
Frequently Asked Questions
What is the severity of GHSA-45x7-px36-x8w8?
GHSA-45x7-px36-x8w8 is considered a high severity vulnerability due to its potential to compromise the integrity of SSH secure channels.
How do I fix GHSA-45x7-px36-x8w8?
To fix GHSA-45x7-px36-x8w8, update the affected software to the recommended versions specified in the advisory.
What types of software are affected by GHSA-45x7-px36-x8w8?
GHSA-45x7-px36-x8w8 affects various software packages including golang.org/x/crypto, paramiko, and russh.
What is the main impact of exploiting GHSA-45x7-px36-x8w8?
Exploiting GHSA-45x7-px36-x8w8 allows an attacker to manipulate messages in the SSH protocol, potentially leading to data integrity issues.
Is there a way to detect GHSA-45x7-px36-x8w8 on my system?
Detection of GHSA-45x7-px36-x8w8 can be done by checking the versions of the affected software packages installed on your system.