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Debian Security Advisory 5588-1
Debian Linux Security Advisory 5588-1 - Fabian Baeumer, Marcus Brinkmann and Joerg Schwenk discovered that the SSH protocol is prone to a prefix truncation attack, known as the "Terrapin attack". This attack allows a MITM attacker to effect a limited break of the integrity of the early encrypted SSH transport protocol by sending extra messages prior to the commencement of encryption, and deleting an equal number of consecutive messages immediately after encryption starts.
-----BEGIN PGP SIGNED MESSAGE-----Hash: SHA512- -------------------------------------------------------------------------Debian Security Advisory DSA-5588-1 [email protected]://www.debian.org/security/ Salvatore BonaccorsoDecember 24, 2023 https://www.debian.org/security/faq- -------------------------------------------------------------------------Package : puttyCVE ID : CVE-2021-36367 CVE-2023-48795Debian Bug : 990901Fabian Baeumer, Marcus Brinkmann and Joerg Schwenk discovered that theSSH protocol is prone to a prefix truncation attack, known as the"Terrapin attack". This attack allows a MITM attacker to effect alimited break of the integrity of the early encrypted SSH transportprotocol by sending extra messages prior to the commencement ofencryption, and deleting an equal number of consecutive messagesimmediately after encryption starts.Details can be found at https://terrapin-attack.com/For the oldstable distribution (bullseye), these problems have been fixedin version 0.74-1+deb11u1. This update includes a fix for CVE-2021-36367.For the stable distribution (bookworm), these problems have been fixed inversion 0.78-2+deb12u1.We recommend that you upgrade your putty packages.For the detailed security status of putty please refer to its securitytracker page at:https://security-tracker.debian.org/tracker/puttyFurther information about Debian Security Advisories, how to applythese updates to your system and frequently asked questions can befound at: https://www.debian.org/security/Mailing list: [email protected] PGP SIGNATURE-----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qdiJ-----END PGP SIGNATURE-----
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### Summary Russh v0.40.1 and earlier is vulnerable to a novel prefix truncation attack (a.k.a. Terrapin attack), which allows a man-in-the-middle attacker to strip an arbitrary number of messages right after the initial key exchange, breaking SSH extension negotiation (RFC8308) in the process and thus downgrading connection security. ### 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. Support for strict key exchange has been added to Russh in the patched version. **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 Ch...