New Terrapin Flaw Could Let Attackers Downgrade SSH Protocol Security

Security scientists from Ruhr University Bochum have found a vulnerability in the Protected Shell (SSH) cryptographic network protocol that could allow an attacker to downgrade the connection’s security by breaking the integrity of the secure channel.

Known as Terrapin (CVE-2023-48795, CVSS rating: 5.9), the exploit has been explained as the “very first at any time nearly exploitable prefix truncation attack.”

“By thoroughly changing the sequence quantities for the duration of the handshake, an attacker can remove an arbitrary sum of messages despatched by the customer or server at the starting of the safe channel devoid of the customer or server noticing it,” scientists Fabian Bäumer, Marcus Brinkmann, and Jörg Schwenk claimed.

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SSH is a process for securely sending commands to a personal computer over an unsecured network. It relies on cryptography to authenticate and encrypt connections involving products.

This is achieved by means of a handshake in which a customer and server agree upon cryptographic primitives and exchange keys essential for location up a secure channel that can deliver confidentiality and integrity assures.

However, a terrible actor in an active adversary-in-the-middle (AitM) place with the potential to intercept and modify the connection’s targeted traffic at the TCP/IP layer can downgrade the security of an SSH connection when using SSH extension negotiation.

“The attack can be executed in practice, making it possible for an attacker to downgrade the connection’s security by truncating the extension negotiation message (RFC8308) from the transcript,” the scientists defined.

“The truncation can lead to making use of a lot less protected consumer authentication algorithms and deactivating precise countermeasures against keystroke timing attacks in OpenSSH 9.5.”

Yet another vital prerequisite required to pulling off the attack is the use of a vulnerable encryption manner this sort of as ChaCha20-Poly1305 or CBC with Encrypt-then-MAC to protected the relationship.

“In a real-environment state of affairs, an attacker could exploit this vulnerability to intercept sensitive information or get management more than critical systems applying administrator privileged accessibility,” Qualys reported. “This risk is significantly acute for organizations with significant, interconnected networks that give entry to privileged details.”

The flaw impacts several SSH shopper and server implementations, this sort of as OpenSSH, Paramiko, PuTTY, KiTTY, WinSCP, libssh, libssh2, AsyncSSH, FileZilla, and Dropbear, prompting the maintainers to launch patches to mitigate prospective challenges.

“Since SSH servers and OpenSSH in specific are so usually utilized through cloud-centered company software environments, it truly is critical for organizations to make certain they have taken ideal steps to patch their servers,” Yair Mizrahi, senior security researcher of security analysis at JFrog, told The Hacker Information.

“Nonetheless, a susceptible customer connecting to a patched server will continue to end result in an vulnerable link. Thus, businesses will have to also just take actions to identify each and every susceptible occurrence throughout their full infrastructure and utilize a mitigation right away.”

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