After six months of development release , an open implementation of a client and server for working with SSH 2.0 and SFTP protocols.
The latest release features a fix for a vulnerability affecting ssh, sshd, ssh-add, and ssh-keygen. The issue exists in the code that parses private keys of the XMSS type and allows an attacker to initiate an integer overflow. This vulnerability is marked as exploitable but not widely applicable, as support for XMSS keys is considered experimental and disabled by default (in the portable version, there isn’t even a build option in autoconf to enable XMSS).
Key Changes:
- In ssh, sshd, and ssh-agent the code prevents the recovery of the private key residing in memory during side-channel attacks such as , and . Private keys are now encrypted when loaded into memory and decrypted only at the moment of use, remaining encrypted at all other times. With this approach, for an attacker to successfully recover a private key, they must first recover a randomly generated 16 KB intermediary key used to encrypt the main key, which is unlikely given the high error rates associated with modern attacks;
- In adds experimental support for a simplified scheme for creating and verifying digital signatures. Digital signatures can be created using regular SSH keys stored on disk or in ssh-agent, and verified using a similar list to authorized_keys . The digital signature embeds namespace information to avoid confusion when used in different contexts (for example, for email and files);
- ssh-keygen is now set by default to use the rsa-sha2-512 algorithm when signing certificates based on an RSA key (when operating in CA mode). Such certificates are incompatible with releases prior to OpenSSH 7.2 (for compatibility, the algorithm type should be overridden, for instance, by invoking 'ssh-keygen -t ssh-rsa -s …');
- In ssh, support for expanding the substitution '%n' (the hostname specified in the address line) has been implemented in the ProxyCommand expression.
- In the lists of encryption algorithms for ssh and sshd, the symbol "^" can now be used to insert default proposed algorithms. For example, to add ssh-ed25519 to the default list, one can specify "HostKeyAlgorithms ^ssh-ed25519";
- In ssh-keygen, the output now includes the comment attached to the key when extracting the public key from the private one;
- In ssh-keygen, the ability to use the flag "-v" has been added when performing key search operations (e.g., "ssh-keygen -vF host"), which will result in the output of a visual host signature;
- Added the ability to use as an alternative format for storing private keys on disk. By default, the PEM format continues to be used, while PKCS8 may be useful for compatibility with third-party applications.
Source: opennet.ru
