OpenSSH 9.8 has just been released. It will be available from the mirrors listed at https://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: https://www.openssh.com/donations.html Security ======== This release contains fixes for two security problems, one critical and one minor. 1) Race condition in sshd(8) A critical vulnerability in sshd(8) was present in Portable OpenSSH versions 8.5p1 and 9.7p1 (inclusive) that may allow arbitrary code execution with root privileges. Successful exploitation has been demonstrated on 32-bit Linux/glibc systems with ASLR. Under lab conditions, the attack requires on average 6-8 hours of continuous connections up to the maximum the server will accept. Exploitation on 64-bit systems is believed to be possible but has not been demonstrated at this time. It's likely that these attacks will be improved upon. Exploitation on non-glibc systems is conceivable but has not been examined. Systems that lack ASLR or users of downstream Linux distributions that have modified OpenSSH to disable per-connection ASLR re-randomisation (yes - this is a thing, no - we don't understand why) may potentially have an easier path to exploitation. OpenBSD is not vulnerable. We thank the Qualys Security Advisory Team for discovering, reporting and demonstrating exploitability of this problem, and for providing detailed feedback on additional mitigation measures. 2) Logic error in ssh(1) ObscureKeystrokeTiming In OpenSSH version 9.5 through 9.7 (inclusive), when connected to an OpenSSH server version 9.5 or later, a logic error in the ssh(1) ObscureKeystrokeTiming feature (on by default) rendered this feature ineffective - a passive observer could still detect which network packets contained real keystrokes when the countermeasure was active because both fake and real keystroke packets were being sent unconditionally. This bug was found by Philippos Giavridis and also independently by Jacky Wei En Kung, Daniel Hugenroth and Alastair Beresford of the University of Cambridge Computer Lab. Worse, the unconditional sending of both fake and real keystroke packets broke another long-standing timing attack mitigation. Since OpenSSH 2.9.9 sshd(8) has sent fake keystoke echo packets for traffic received on TTYs in echo-off mode, such as when entering a password into su(8) or sudo(8). This bug rendered these fake keystroke echoes ineffective and could allow a passive observer of a SSH session to once again detect when echo was off and obtain fairly limited timing information about keystrokes in this situation (20ms granularity by default). This additional implication of the bug was identified by Jacky Wei En Kung, Daniel Hugenroth and Alastair Beresford and we thank them for their detailed analysis. This bug does not affect connections when ObscureKeystrokeTiming was disabled or sessions where no TTY was requested. Future deprecation notice ========================= OpenSSH plans to remove support for the DSA signature algorithm in early 2025. This release disables DSA by default at compile time. DSA, as specified in the SSHv2 protocol, is inherently weak - being limited to a 160 bit private key and use of the SHA1 digest. Its estimated security level is only 80 bits symmetric equivalent. OpenSSH has disabled DSA keys by default since 2015 but has retained run-time optional support for them. DSA was the only mandatory-to- implement algorithm in the SSHv2 RFCs, mostly because alternative algorithms were encumbered by patents when the SSHv2 protocol was specified. This has not been the case for decades at this point and better algorithms are well supported by all actively-maintained SSH implementations. We do not consider the costs of maintaining DSA in OpenSSH to be justified and hope that removing it from OpenSSH can accelerate its wider deprecation in supporting cryptography libraries. This release, and its deactivation of DSA by default at compile-time, marks the second step in our timeline to finally deprecate DSA. The final step of removing DSA support entirely is planned for the first OpenSSH release of 2025. DSA support may be re-enabled in OpenBSD by setting "DSAKEY=yes" in Makefile.inc. To enable DSA support in portable OpenSSH, pass the "--enable-dsa-keys" option to configure. Potentially-incompatible changes -------------------------------- * all: as mentioned above, the DSA signature algorithm is now disabled at compile time. * sshd(8): the server will now block client addresses that repeatedly fail authentication, repeatedly connect without ever completing authentication or that crash the server. See the discussion of PerSourcePenalties below for more information. Operators of servers that accept connections from many users, or servers that accept connections from addresses behind NAT or proxies may need to consider these settings. * sshd(8): the server has been split into a listener binary, sshd(8), and a per-session binary "sshd-session". This allows for a much smaller listener binary, as it no longer needs to support the SSH protocol. As part of this work, support for disabling privilege separation (which previously required code changes to disable) and disabling re-execution of sshd(8) has been removed. Further separation of sshd-session into additional, minimal binaries is planned for the future. * sshd(8): several log messages have changed. In particular, some log messages will be tagged with as originating from a process named "sshd-session" rather than "sshd". * ssh-keyscan(1): this tool previously emitted comment lines containing the hostname and SSH protocol banner to standard error. This release now emits them to standard output, but adds a new "-q" flag to silence them altogether. * sshd(8): (portable OpenSSH only) sshd will no longer use argv[0] as the PAM service name. A new "PAMServiceName" sshd_config(5) directive allows selecting the service name at runtime. This defaults to "sshd". bz2101 * (portable OpenSSH only) Automatically-generated files, such as configure, config.h.in, etc will now be checked in to the portable OpenSSH git release branch (e.g. V_9_8). This should ensure that the contents of the signed release branch exactly match the contents of the signed release tarball. Changes since OpenSSH 9.7 ========================= This release contains mostly bugfixes. New features ------------ * sshd(8): as described above, sshd(8) will now penalise client addresses that, for various reasons, do not successfully complete authentication. This feature is controlled by a new sshd_config(5) PerSourcePenalties option and is on by default. sshd(8) will now identify situations where the session did not authenticate as expected. These conditions include when the client repeatedly attempted authentication unsucessfully (possibly indicating an attack against one or more accounts, e.g. password guessing), or when client behaviour caused sshd to crash (possibly indicating attempts to exploit bugs in sshd). When such a condition is observed, sshd will record a penalty of some duration (e.g. 30 seconds) against the client's address. If this time is above a minimum configurable threshold, then all connections from the client address will be refused (along with any others in the same PerSourceNetBlockSize CIDR range) until the penalty expire. Repeated offenses by the same client address will accrue greater penalties, up to a configurable maximum. Address ranges may be fully exempted from penalties, e.g. to guarantee access from a set of trusted management addresses, using the new sshd_config(5) PerSourcePenaltyExemptList option. We hope these options will make it significantly more difficult for attackers to find accounts with weak/guessable passwords or exploit bugs in sshd(8) itself. This option is enabled by default. * ssh(8): allow the HostkeyAlgorithms directive to disable the implicit fallback from certificate host key to plain host keys. Bugfixes -------- * misc: fix a number of inaccuracies in the PROTOCOL.* documentation files. GHPR430 GHPR487 * all: switch to strtonum(3) for more robust integer parsing in most places. * ssh(1), sshd(8): correctly restore sigprocmask around ppoll() * ssh-keysign(8): stricter validation of messaging socket fd GHPR492 * sftp(1): flush stdout after writing "sftp>" prompt when not using editline. GHPR480 * sftp-server(8): fix home-directory extension implementation, it previously always returned the current user's home directory contrary to the spec. GHPR477 * ssh-keyscan(1): do not close stdin to prevent error messages when stdin is read multiple times. E.g. echo localhost | ssh-keyscan -f - -f - * regression tests: fix rekey test that was testing the same KEX algorithm repeatedly instead of testing all of them. bz3692 * ssh_config(5), sshd_config(5): clarify the KEXAlgorithms directive documentation, especially around what is supported vs available. bz3701. Portability ----------- * sshd(8): expose SSH_AUTH_INFO_0 always to PAM auth modules unconditionally. The previous behaviour was to expose it only when particular authentication methods were in use. * build: fix OpenSSL ED25519 support detection. An incorrect function signature in configure.ac previously prevented enabling the recently added support for ED25519 private keys in PEM PKCS8 format. * ssh(1), ssh-agent(8): allow the presence of the WAYLAND_DISPLAY environment variable to enable SSH_ASKPASS, similarly to the X11 DISPLAY environment variable. GHPR479 * build: improve detection of the -fzero-call-used-regs compiler flag. bz3673. * build: relax OpenSSL version check to accept all OpenSSL 3.x versions. * sshd(8): add support for notifying systemd on server listen and reload, using a standalone implementation that doesn't depend on libsystemd. bz2641 Checksums: ========== - SHA1 (openssh-9.8.tar.gz) = bc45cedae7f70b41e9922ef4c9f56e74b9a659b7 - SHA256 (openssh-9.8.tar.gz) = Dnc69VLWFBFdiaz8wySPlvHjb7wZfh/kblQ8ISuQr1Y= - SHA1 (openssh-9.8p1.tar.gz) = a0bb501b11349f5c5c33a269351be091dc2c2727 - SHA256 (openssh-9.8p1.tar.gz) = 3YvQAqN5tdSZ37BQ3R+pr4Ap6ARh9LtsUjxJlz9aOfM= 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 from the mirror sites: https://cdn.openbsd.org/pub/OpenBSD/OpenSSH/RELEASE_KEY.asc Reporting Bugs: =============== - Please read https://www.openssh.com/report.html Security bugs should be reported directly to openssh@xxxxxxxxxxx _______________________________________________ openssh-unix-dev mailing list openssh-unix-dev@xxxxxxxxxxx https://lists.mindrot.org/mailman/listinfo/openssh-unix-dev
