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Vol. 1 · Ed. 2026
CyberGlossary
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Entry № 1260

Terrapin Attack (CVE-2023-48795)

Was ist Terrapin Attack (CVE-2023-48795)?

Terrapin Attack (CVE-2023-48795)A 2023 prefix-truncation flaw in the SSH transport protocol that allows an active network attacker to silently downgrade or strip extensions during the handshake, weakening features like keystroke timing protection.

The Terrapin attack (CVE-2023-48795), disclosed by Bäumer, Brinkmann, and Schwenk in December 2023, is a prefix-truncation flaw in the SSH binary packet protocol. By manipulating packet sequence numbers during the initial KEX handshake — specifically when ChaCha20-Poly1305 (`chacha20-poly1305@openssh.com`) or CBC-EtM ciphers are used — a man-in-the-middle attacker can truncate the secure channel's initial messages without the integrity check failing, causing both ends to disagree about which extensions were negotiated. The most cited practical impact is silently disabling extensions such as keystroke-timing obfuscation; the underlying primitive can also weaken implementation-specific authentication features (notably AsyncSSH's CVE-2023-46446). Terrapin spurred quick fixes: OpenSSH 9.6 introduced a strict KEX mode that resets sequence numbers, and most major SSH implementations (Dropbear, libssh, PuTTY, Bitvise, Cisco IOS) followed. Mitigation is to upgrade clients and servers so both negotiate `strict-kex`, and to prefer AES-GCM ciphers, which are unaffected.

● Beispiele

  1. 01

    An attacker positioned between two SSH peers truncates the KEX handshake so a keystroke-timing extension never gets negotiated, then mounts a timing attack on the user's password.

  2. 02

    An infrastructure team rolls out OpenSSH 9.6 across all jump hosts; the new `strict-kex` negotiation reports `kex_strict_s_v00@openssh.com` and blocks the truncation primitive.

● Häufige Fragen

Was ist Terrapin Attack (CVE-2023-48795)?

A 2023 prefix-truncation flaw in the SSH transport protocol that allows an active network attacker to silently downgrade or strip extensions during the handshake, weakening features like keystroke timing protection. Es gehört zur Kategorie Angriffe und Bedrohungen der Cybersicherheit.

Was bedeutet Terrapin Attack (CVE-2023-48795)?

A 2023 prefix-truncation flaw in the SSH transport protocol that allows an active network attacker to silently downgrade or strip extensions during the handshake, weakening features like keystroke timing protection.

Wie funktioniert Terrapin Attack (CVE-2023-48795)?

The Terrapin attack (CVE-2023-48795), disclosed by Bäumer, Brinkmann, and Schwenk in December 2023, is a prefix-truncation flaw in the SSH binary packet protocol. By manipulating packet sequence numbers during the initial KEX handshake — specifically when ChaCha20-Poly1305 (`chacha20-poly1305@openssh.com`) or CBC-EtM ciphers are used — a man-in-the-middle attacker can truncate the secure channel's initial messages without the integrity check failing, causing both ends to disagree about which extensions were negotiated. The most cited practical impact is silently disabling extensions such as keystroke-timing obfuscation; the underlying primitive can also weaken implementation-specific authentication features (notably AsyncSSH's CVE-2023-46446). Terrapin spurred quick fixes: OpenSSH 9.6 introduced a strict KEX mode that resets sequence numbers, and most major SSH implementations (Dropbear, libssh, PuTTY, Bitvise, Cisco IOS) followed. Mitigation is to upgrade clients and servers so both negotiate `strict-kex`, and to prefer AES-GCM ciphers, which are unaffected.

Wie schützt man sich gegen Terrapin Attack (CVE-2023-48795)?

Schutzmaßnahmen gegen Terrapin Attack (CVE-2023-48795) kombinieren typischerweise technische Kontrollen und operative Praktiken, wie in der Definition oben beschrieben.

Welche anderen Bezeichnungen gibt es für Terrapin Attack (CVE-2023-48795)?

Übliche alternative Bezeichnungen: CVE-2023-48795, SSH prefix truncation.

● Verwandte Begriffe