For compatibility with SSH software which does not support strict key exchange or AES GCM, an algorithm combination such as AES CTR with non-ETM data integrity protection may continue to be acceptable. If this is not possible, the data integrity protection algorithms which are not named -etm are not entirely immune, but are also not believed to be practically exploitable. Users who are committed to older SSH software versions should consider using AES GCM. The encryption algorithms aes256-gcm and aes128-gcm are substantially immune from this attack. Nevertheless, we suggest updating all SSH software to new versions that support strict key exchange. These are the newer data integrity protection algorithms whose names contain -etm.īitvise software versions 8.xx and older are not substantially affected because they do not implement algorithms where this issue is practically exploitable. If you must interoperate with SSH software which does not support strict key exchange, consider disabling the encryption algorithm ChaCha20-Poly1305, as well as integrity algorithms of type encrypt-then-MAC. Other SSH software authors are also releasing new versions to support this. The SSH client and server must both implement strict key exchange for mitigation to be effective. This is a new SSH protocol feature which mitigates this attack. However, it is a cryptographic weakness to address.īitvise software versions 9.32 and newer support strict key exchange. Since the attacker can only remove packets sent before user authentication, this does not seem to fatally break the security of the SSH connection. This affects extensions with security impact, such as server-sig-algs. This can be used to sabotage SSH extension negotiation. Terrapin - CVE-2023-48795: Researchers have identified an issue where all SSH connections which use the encryption algorithm ChaCha20-Poly1305, or any integrity algorithm of type encrypt-then-MAC, are vulnerable to packet sequence manipulation by an active attacker, if the attacker can intercept the network path. The minimum upgrade access expiry date to activate this version is January 1, 2022. This version continues the upgrade access amnesty introduced in version 9.25, so it can be used with any license that is valid for a previous SSH Server 9.xx version. For issues that might arise using the latest SSH Server versions, see Known issues.Ĭhanges in Bitvise SSH Server 9.32:
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