Openssh is een implementatie van het ssh-protocol. Applicaties zoals telnet en rlogin versturen gegevens onversleuteld over het netwerk, waardoor login- en andere gegevens op een eenvoudige manier zijn uit te lezen. Door over te stappen op ssh worden de gegevens versleuteld verstuurd, zodat er geen eavesdropping, connection hijacking en andere aanvallen meer mogelijk zijn. Het ontwikkelteam heeft versie 5.1 uitgebracht en als volgt aangekondigd:
OpenSSH 5.1 has just been released. It will be available from the mirrors listed at http://www.openssh.com/ shortly. We have also recently completed another Internet SSH usage scan, the results of which may be found here. Once again, we would like to thank the OpenSSH community for their continued support of the project, especially those who contributed code or patches, reported bugs, tested snapshots or donated to the project.
- sshd(8): Avoid X11 man-in-the-middle attack on HP/UX (and possibly other platforms) when X11UseLocalhost=no. When attempting to bind(2) to a port that has previously been bound with SO_REUSEADDR set, most operating systems check that either the effective user-id matches the previous bind (common on BSD-derived systems) or that the bind addresses do not overlap (Linux and Solaris). Some operating systems, such as HP/UX, do not perform these checks and are vulnerable to an X11 man-in-the-middle attack when the sshd_config(5) option X11UseLocalhost has been set to "no" - an attacker may establish a more-specific bind, which will be used in preference to sshd's wildcard listener. Modern BSD operating systems, Linux, OS X and Solaris implement the above checks and are not vulnerable to this attack, nor are systems where the X11UseLocalhost has been left at the default value of "yes". Portable OpenSSH 5.1 avoids this problem for all operating systems by not setting SO_REUSEADDR when X11UseLocalhost is set to no. This vulnerability was reported by sway2004009 AT hotmail.com.
Bug and documentation fixes
- Introduce experimental SSH Fingerprint ASCII Visualisation to ssh(1) and ssh-keygen(1). Visual fingerprinnt display is controlled by a new ssh_config(5) option "VisualHostKey". The intent is to render SSH host keys in a visual form that is amenable to easy recall and rejection of changed host keys. This technique inspired by the graphical hash visualisation schemes known as "random art[*]", and by Dan Kaminsky's musings at 23C3 in Berlin. Fingerprint visualisation in is currently disabled by default, as the algorithm used to generate the random art is still subject to change.
[*] "Hash Visualization: a New Technique to improve Real-World Security", Perrig A. and Song D., 1999, International Workshop on Cryptographic Techniques and E-Commerce (CrypTEC '99)
- sshd_config(5) now supports CIDR address/masklen matching in "Match address" blocks, with a fallback to classic wildcard matching. For example:
Match address 192.0.2.0/24,3ffe:ffff::/32,!10.* PasswordAuthentication yes
- sshd(8) now supports CIDR matching in ~/.ssh/authorized_keys from="..." restrictions, also with a fallback to classic wildcard matching.
- Added an extended test mode (-T) to sshd(8) to request that it write its effective configuration to stdout and exit. Extended test mode also supports the specification of connection parameters (username, source address and hostname) to test the application of sshd_config(5) Match rules.
- ssh(1) now prints the number of bytes transferred and the overall connection throughput for SSH protocol 2 sessions when in verbose mode (previously these statistics were displayed for protocol 1 connections only).
- sftp-server(8) now supports extension methods firstname.lastname@example.org and email@example.com that implement statvfs(2)-like operations. (bz#1399)
- sftp(1) now has a "df" command to the sftp client that uses the firstname.lastname@example.org to produce a df(1)-like display of filesystem space and inode utilisation (requires email@example.com support on the server)
- Added a MaxSessions option to sshd_config(5) to allow control of the number of multiplexed sessions supported over a single TCP connection. This allows increasing the number of allowed sessions above the previous default of 10, disabling connection multiplexing (MaxSessions=1) or disallowing login/shell/subsystem sessions entirely (MaxSessions=0).
- Added a firstname.lastname@example.org global request extension that is sent from ssh(1) to sshd(8) when the client knows that it will never request another session (i.e. when session multiplexing is disabled). This allows a server to disallow further session requests and terminate the session in cases where the client has been hijacked.
- ssh-keygen(1) now supports the use of the -l option in combination with -F to search for a host in ~/.ssh/known_hosts and display its fingerprint.
- ssh-keyscan(1) now defaults to "rsa" (protocol 2) keys, instead of "rsa1".
- Added an AllowAgentForwarding option to sshd_config(8) to control whether authentication agent forwarding is permitted. Note that this is a loose control, as a client may install their own unofficial forwarder.
- ssh(1) and sshd(8): avoid unnecessary malloc/copy/free when receiving network data, resulting in a ~10% speedup
- ssh(1) and sshd(8) will now try additional addresses when connecting to a port forward destination whose DNS name resolves to more than one address. The previous behaviour was to try the only first address and give up if that failed. (bz#383)
- ssh(1) and sshd(8) now support signalling that channels are half-closed for writing, through a channel protocol extension notification "email@example.com". This allows propagation of closed file descriptors, so that commands such as: "ssh -2 localhost od /bin/ls | true" do not send unnecessary data over the wire. (bz#85)
- sshd(8): increased the default size of ssh protocol 1 ephemeral keys from 768 to 1024 bits.
- When ssh(1) has been requested to fork after authentication ("ssh -f") with ExitOnForwardFailure enabled, delay the fork until after replies for any -R forwards have been seen. Allows for robust detection of -R forward failure when using -f. (bz#92)
- "Match group" blocks in sshd_config(5) now support negation of groups. E.g. "Match group staff,!guests" (bz#1315)
- sftp(1) and sftp-server(8) now allow chmod-like operations to set set[ug]id/sticky bits. (bz#1310)
- The MaxAuthTries option is now permitted in sshd_config(5) match blocks.
- Multiplexed ssh(1) sessions now support a subset of the ~ escapes that are available to a primary connection. (bz#1331)
- ssh(1) connection multiplexing will now fall back to creating a new connection in most error cases. (bz#1439 bz#1329)
- Added some basic interoperability tests against Twisted Conch.
- Documented OpenSSH's extensions to and deviations from the published SSH protocols (the PROTOCOL file in the distribution)
- Documented OpenSSH's ssh-agent protocol (PROTOCOL.agent).
Portable OpenSSH-specific bugfixes
- Make ssh(1) deal more gracefully with channel requests that fail. Previously it would optimistically assume that requests would always succeed, which could cause hangs if they did not (e.g. when the server runs out of file descriptors). (bz#1384)
- ssh(1) now reports multiplexing errors via the multiplex slave's stderr where possible (subject to LogLevel in the mux master).
- ssh(1) and sshd(8) now send terminate protocol banners with CR+LF for protocol 2 to comply with RFC 4253. Previously they were terminated with CR alone. Protocol 1 banners remain CR terminated. (bz#1443)
- Merged duplicate authentication file checks in sshd(8) and refuse to read authorised_keys and .shosts from non-regular files. (bz#1438)
- Ensure that sshd(8)'s umask disallows at least group and world write, even if a more permissive one has been inherited. (bz#1433)
- Suppress the warning message from sshd(8) when changing to a non-existent user home directory after chrooting. (bz#1461)
- Mention that scp(1) follows symlinks when performing recursive copies. (bz#1466)
- Prevent sshd(8) from erroneously applying public key restrictions leaned from ~/.ssh/authorized_keys to other authentication methods when public key authentication subsequently fails. (bz#1472)
- Fix protocol keepalive timeouts - in some cases, keepalive packets were being sent, but the connection was not being closed when the limit for missing replies was exceeded. (bz#1465)
- Fix ssh(1) sending invalid TTY modes when a TTY was forced (ssh -tt) but stdin was not a TTY. (bz#1199)
- ssh(1) will now exit with a non-zero exit status if ExitOnForwardFailure was set and forwardings were disabled due to a failed host key check.
- Fix MaxAuthTries tests to disallow a free authentication try to clients that skipped the protocol 2 "none" authentication method. (part of bz#1432)
- Make keepalive timeouts apply while synchronously waiting for a packet, particularly during key renegotiation. (bz#1363)
- sshd(8) has been audited to eliminate fd leaks and calls to fatal() in conditions of file descriptor exhaustion.
- Avoid a sshd(8) hang-on-exit on Solaris caused by depending on the success of isatty() on a PTY master (undefined behaviour). Probably affected other platforms too. (bz#1463)
- Fixed test for locked accounts on HP/UX with shadowed passwords disabled. (bz#1083
- Disable poll() fallback in atomiciov for Tru64. readv doesn't seem to be a comparable object there, which lead to compilation errors. (bz#1386)
- Fall back to racy rename if link returns EXDEV. (bz#1447)
- Explicitly handle EWOULDBLOCK wherever we handle EAGAIN, on some platforms (HP nonstop) it is a distinct errno. (bz#1467)
- Avoid NULL dereferences in ancient sigaction replacement code. (bz#1240)
- Avoid linking against libgssapi, which despite its name doesn't seem to implement all of GSSAPI. (bz#1276)
- Use explicit noreturn attribute instead of __dead, fixing compilation problems on Interix. (bz#1112)
- Added support password expiry on Tru64 SIA systems. (bz#1241)
- Fixed an UMAC alignment problem that manifested on Itanium platforms. (bz#1462)
- The sftp-server(8) manual now describes the requirements for transfer logging in chroot environments. (bz#1488)
- Strip trailing dot from hostnames when the sshd_config(5) HostbasedUsesNameFromPacketOnly option is set. (bz#1200)