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AUSCERT External Security Bulletin Redistribution
Multiple vulnerabilities identified in OpenSSH prior to version 7.8
24 August 2018
AusCERT Security Bulletin Summary
Operating System: Windows
UNIX variants (UNIX, Linux, OSX)
Impact/Access: Denial of Service -- Remote/Unauthenticated
Access Confidential Data -- Remote/Unauthenticated
Reduced Security -- Remote/Unauthenticated
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OpenSSH 7.8 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 2.0 implementation and
includes sftp client and server support.
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:
This release includes a number of changes that may affect existing
* ssh-keygen(1): write OpenSSH format private keys by default
instead of using OpenSSL's PEM format. The OpenSSH format,
supported in OpenSSH releases since 2014 and described in the
PROTOCOL.key file in the source distribution, offers substantially
better protection against offline password guessing and supports
key comments in private keys. If necessary, it is possible to write
old PEM-style keys by adding "-m PEM" to ssh-keygen's arguments
when generating or updating a key.
* sshd(8): remove internal support for S/Key multiple factor
authentication. S/Key may still be used via PAM or BSD auth.
* ssh(1): remove vestigal support for running ssh(1) as setuid. This
used to be required for hostbased authentication and the (long
gone) rhosts-style authentication, but has not been necessary for
a long time. Attempting to execute ssh as a setuid binary, or with
uid != effective uid will now yield a fatal error at runtime.
* sshd(8): the semantics of PubkeyAcceptedKeyTypes and the similar
HostbasedAcceptedKeyTypes options have changed. These now specify
signature algorithms that are accepted for their respective
authentication mechanism, where previously they specified accepted
key types. This distinction matters when using the RSA/SHA2
signature algorithms "rsa-sha2-256", "rsa-sha2-512" and their
certificate counterparts. Configurations that override these
options but omit these algorithm names may cause unexpected
authentication failures (no action is required for configurations
that accept the default for these options).
* sshd(8): the precedence of session environment variables has
changed. ~/.ssh/environment and environment="..." options in
authorized_keys files can no longer override SSH_* variables set
implicitly by sshd.
* ssh(1)/sshd(8): the default IPQoS used by ssh/sshd has changed.
They will now use DSCP AF21 for interactive traffic and CS1 for
bulk. For a detailed rationale, please see the commit message:
Changes since OpenSSH 7.7
This is primarily a bugfix release.
* ssh(1)/sshd(8): add new signature algorithms "rsa-sha2-256-cert-
firstname.lastname@example.org" and "email@example.com" to
explicitly force use of RSA/SHA2 signatures in authentication.
* sshd(8): extend the PermitUserEnvironment option to accept a
whitelist of environment variable names in addition to global
"yes" or "no" settings.
* sshd(8): add a PermitListen directive to sshd_config(5) and a
corresponding permitlisten= authorized_keys option that control
which listen addresses and port numbers may be used by remote
forwarding (ssh -R ...).
* sshd(8): add some countermeasures against timing attacks used for
account validation/enumeration. sshd will enforce a minimum time
or each failed authentication attempt consisting of a global 5ms
minimum plus an additional per-user 0-4ms delay derived from a
* sshd(8): add a SetEnv directive to allow an administrator to
explicitly specify environment variables in sshd_config.
Variables set by SetEnv override the default and client-specified
* ssh(1): add a SetEnv directive to request that the server sets
an environment variable in the session. Similar to the existing
SendEnv option, these variables are set subject to server
* ssh(1): allow "SendEnv -PATTERN" to clear environment variables
previously marked for sending to the server. bz#1285
* ssh(1)/sshd(8): make UID available as a %-expansion everywhere
that the username is available currently. bz#2870
* ssh(1): allow setting ProxyJump=none to disable ProxyJump
* sshd(8): avoid observable differences in request parsing that could
be used to determine whether a target user is valid.
* all: substantial internal refactoring
* ssh(1)/sshd(8): fix some memory leaks; bz#2366
* ssh(1): fix a pwent clobber (introduced in openssh-7.7) that could
occur during key loading, manifesting as crash on some platforms.
* sshd_config(5): clarify documentation for AuthenticationMethods
* ssh(1): ensure that the public key algorithm sent in a
public key SSH_MSG_USERAUTH_REQUEST matches the content of the
signature blob. Previously, these could be inconsistent when a
legacy or non-OpenSSH ssh-agent returned a RSA/SHA1 signature
when asked to make a RSA/SHA2 signature.
* sshd(8): fix failures to read authorized_keys caused by faulty
supplemental group caching. bz#2873
* scp(1): apply umask to directories, fixing potential mkdir/chmod
race when copying directory trees bz#2839
* ssh-keygen(1): return correct exit code when searching for and
hashing known_hosts entries in a single operation; bz#2772
* ssh(1): prefer the ssh binary pointed to via argv to $PATH when
re-executing ssh for ProxyJump. bz#2831
* sshd(8): do not ban PTY allocation when a sshd session is
restricted because the user password is expired as it breaks
password change dialog. (regression in openssh-7.7).
* ssh(1)/sshd(8): fix error reporting from select() failures.
* ssh(1): improve documentation for -w (tunnel) flag, emphasising
that -w implicitly sets Tunnel=point-to-point. bz#2365
* ssh-agent(1): implement EMFILE mitigation for ssh-agent. ssh-agent
will no longer spin when its file descriptor limit is exceeded.
* ssh(1)/sshd(8): disable SSH2_MSG_DEBUG messages for Twisted Conch
clients. Twisted Conch versions that lack a version number in
their identification strings will mishandle these messages when
running on Python 2.x (https://twistedmatrix.com/trac/ticket/9422)
* sftp(1): notify user immediately when underlying ssh process dies
* ssh(1)/sshd(8): fix tunnel forwarding; regression in 7.7 release.
* ssh-agent(1): don't kill ssh-agent's listening socket entirely if
it fails to accept(2) a connection. bz#2837
* sshd(8): relax checking of authorized_keys environment="..."
options to allow underscores in variable names (regression
introduced in 7.7). bz#2851
* ssh(1): add some missing options in the configuration dump output
(ssh -G). bz#2835
* sshd(8): Expose details of completed authentication to PAM auth
modules via SSH_AUTH_INFO_0 in the PAM environment. bz#2408
* Fix compilation problems caused by fights between zlib and OpenSSL
colliding uses of "free_func"
* Improve detection of unsupported compiler options. Recently these
may have manifested as "unsupported -Wl,-z,retpoline" warnings
* sshd(8): some sandbox support for Linux/s390 bz#2752.
* regress tests: unbreak key-options.sh test on platforms without
* use getrandom(2) for PRNG seeding when built without OpenSSL.
- - SHA1 (openssh-7.8.tar.gz) = ed5511cd42b543cd15166a9cbc56705f23b847e7
- - SHA256 (openssh-7.8.tar.gz) = TDqIsMEmghsBUNCrSCPyCxChfitntyOLXNC694py1XE
- - SHA1 (openssh-7.8p1.tar.gz) = 27e267e370315561de96577fccae563bc2c37a60
- - SHA256 (openssh-7.8p1.tar.gz) = GkhLsVFSwYO7JRThEqow3TQTjDz7Ay7uVJCmbFBxRMo
Please note that the SHA256 signatures are base64 encoded and not
hexadecimal (which is the default for most checksum tools). The PGP
key used to sign the releases is available as RELEASE_KEY.asc from
the mirror sites.
- - Please read http://www.openssh.com/report.html
Security bugs should be reported directly to firstname.lastname@example.org
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