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AUSCERT External Security Bulletin Redistribution
ESB-2008.0721 -- [HP-UX]
OpenSSH 5.1 release fixes possible man-in-the-middle attack
22 July 2008
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AusCERT Security Bulletin Summary
---------------------------------
Product: OpenSSH
Publisher: OpenSSH
Operating System: HP-UX
Impact: Reduced Security
Access: Remote/Unauthenticated
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OpenSSH 5.1 has just been released. It will be available from the
mirrors listed at http://www.openssh.com/ shortly.
OpenSSH is a 100% complete SSH protocol version 1.3, 1.5 and 2.0
implementation and includes sftp client and server support.
We have also recently completed another Internet SSH usage scan, the
results of which may be found at http://www.openssh.com/usage.html
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. More information on donations may be found at:
http://www.openssh.com/donations.html
Changes since OpenSSH 5.0
=========================
Security:
* 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.
New features:
* 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)
http://sparrow.ece.cmu.edu/~adrian/projects/validation/validation.pdf
* 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 statvfs@openssh.com and
fstatvfs@openssh.com that implement statvfs(2)-like operations.
(bz#1399)
* sftp(1) now has a "df" command to the sftp client that uses the
statvfs@openssh.com to produce a df(1)-like display of filesystem
space and inode utilisation (requires statvfs@openssh.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 no-more-sessions@openssh.com 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 "eow@openssh.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).
Bug and documentation fixes
* 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.
Portable OpenSSH-specific bugfixes
* 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)
Checksums:
==========
- SHA1 (openssh-5.1.tar.gz) = 1e5b43844ed015e4fbbbe25cfad6f5377c60e759
- SHA1 (openssh-5.1p1.tar.gz) = 877ea5b283060fe0160e376ea645e8e168047ff5
Reporting Bugs:
===============
- - Please read http://www.openssh.com/report.html
Security bugs should be reported directly to openssh@openssh.com
OpenSSH is brought to you by Markus Friedl, Niels Provos, Theo de Raadt,
Kevin Steves, Damien Miller, Darren Tucker, Jason McIntyre, Tim Rice and
Ben Lindstrom.
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