OpenSSH 8.6 released
Note that the deactivation of "ssh-rsa" signatures does not necessarily require cessation of use for RSA keys. In the SSH protocol, keys may be capable of signing using multiple algorithms. In particular, "ssh-rsa" keys are capable of signing using "rsa-sha2-256" (RSA/SHA256), "rsa-sha2-512" (RSA/SHA512) and "ssh-rsa" (RSA/SHA1). Only the last of these is being turned off by default."
From: | Damien Miller <djm-AT-cvs.openbsd.org> | |
To: | lwn-AT-lwn.net | |
Subject: | Announce: OpenSSH 8.6 released | |
Date: | Sun, 18 Apr 2021 18:53:14 -0600 | |
Message-ID: | <94b0350a0f8a1fac@cvs.openbsd.org> |
OpenSSH 8.6 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 Future deprecation notice ========================= It is now possible[1] to perform chosen-prefix attacks against the SHA-1 algorithm for less than USD$50K. In the SSH protocol, the "ssh-rsa" signature scheme uses the SHA-1 hash algorithm in conjunction with the RSA public key algorithm. OpenSSH will disable this signature scheme by default in the near future. Note that the deactivation of "ssh-rsa" signatures does not necessarily require cessation of use for RSA keys. In the SSH protocol, keys may be capable of signing using multiple algorithms. In particular, "ssh-rsa" keys are capable of signing using "rsa-sha2-256" (RSA/SHA256), "rsa-sha2-512" (RSA/SHA512) and "ssh-rsa" (RSA/SHA1). Only the last of these is being turned off by default. This algorithm is unfortunately still used widely despite the existence of better alternatives, being the only remaining public key signature algorithm specified by the original SSH RFCs that is still enabled by default. The better alternatives include: * The RFC8332 RSA SHA-2 signature algorithms rsa-sha2-256/512. These algorithms have the advantage of using the same key type as "ssh-rsa" but use the safe SHA-2 hash algorithms. These have been supported since OpenSSH 7.2 and are already used by default if the client and server support them. * The RFC8709 ssh-ed25519 signature algorithm. It has been supported in OpenSSH since release 6.5. * The RFC5656 ECDSA algorithms: ecdsa-sha2-nistp256/384/521. These have been supported by OpenSSH since release 5.7. To check whether a server is using the weak ssh-rsa public key algorithm, for host authentication, try to connect to it after removing the ssh-rsa algorithm from ssh(1)'s allowed list: ssh -oHostKeyAlgorithms=-ssh-rsa user@host If the host key verification fails and no other supported host key types are available, the server software on that host should be upgraded. OpenSSH recently enabled the UpdateHostKeys option by default to assist the client by automatically migrating to better algorithms. [1] "SHA-1 is a Shambles: First Chosen-Prefix Collision on SHA-1 and Application to the PGP Web of Trust" Leurent, G and Peyrin, T (2020) https://eprint.iacr.org/2020/014.pdf Security ======== * sshd(8): OpenSSH 8.5 introduced the LogVerbose keyword. When this option was enabled with a set of patterns that activated logging in code that runs in the low-privilege sandboxed sshd process, the log messages were constructed in such a way that printf(3) format strings could effectively be specified the low-privilege code. An attacker who had sucessfully exploited the low-privilege process could use this to escape OpenSSH's sandboxing and attack the high-privilege process. Exploitation of this weakness is highly unlikely in practice as the LogVerbose option is not enabled by default and is typically only used for debugging. No vulnerabilities in the low-privilege process are currently known to exist. Thanks to Ilja Van Sprundel for reporting this bug. Changes since OpenSSH 8.5 ========================= This release contains mostly bug fixes. New features ------------ * sftp-server(8): add a new limits@openssh.com protocol extension that allows a client to discover various server limits, including maximum packet size and maximum read/write length. * sftp(1): use the new limits@openssh.com extension (when available) to select better transfer lengths in the client. * sshd(8): Add ModuliFile keyword to sshd_config to specify the location of the "moduli" file containing the groups for DH-GEX. * unit tests: Add a TEST_SSH_ELAPSED_TIMES environment variable to enable printing of the elapsed time in seconds of each test. Bugfixes -------- * ssh_config(5), sshd_config(5): sync CASignatureAlgorithms lists in manual pages with the current default. GHPR#174 * ssh(1): ensure that pkcs11_del_provider() is called before exit. GHPR#234 * ssh(1), sshd(8): fix problems in string->argv conversion. Multiple backslashes were not being dequoted correctly and quoted space in the middle of a string was being incorrectly split. GHPR#223 * ssh(1): return non-zero exit status when killed by signal; bz#3281 * sftp-server(8): increase maximum SSH2_FXP_READ to match the maximum packet size. Also handle zero-length reads that are not explicitly banned by the spec. Portability ----------- * sshd(8): don't mistakenly exit on transient read errors on the network socket (e.g. EINTR, EAGAIN); bz3297 * Create a dedicated contrib/gnome-ssk-askpass3.c source instead of building it from the same file as used for GNOME2. Use the GNOME3 gdk_seat_grab() to manage keyboard/mouse/server grabs for better compatibility with Wayland. * Fix portability build errors bz3293 bz3292 bz3291 bz3278 * sshd(8): soft-disallow the fstatat64 syscall in the Linux seccomp-bpf sandbox. bz3276 * unit tests: enable autoopt and misc unit tests that were previously skipped Checksums: ========== - SHA1 (openssh-8.6.tar.gz) = a3e93347eed6296faaaceb221e8786391530fccb - SHA256 (openssh-8.6.tar.gz) = ihmgdEgKfCBRpC0qzdQRwYownrpBf+rsihvk4Rmim8M= - SHA1 (openssh-8.6p1.tar.gz) = 8f9f0c94317baeb97747d6258f3997b4542762c0 - SHA256 (openssh-8.6p1.tar.gz) = w+bk2hYhdiyFDQO0fu0eSN/0zJYI3etUcgKiNN+O164= 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 Please note that the OpenPGP key used to sign releases has been rotated for this release. The new key has been signed by the previous key to provide continuity. Reporting Bugs: =============== - Please read https://www.openssh.com/report.html Security bugs should be reported directly to openssh@openssh.com
(Log in to post comments)
OpenSSH 8.6 released
Posted Apr 20, 2021 7:14 UTC (Tue) by wtarreau (subscriber, #51152) [Link]
SSH is widely used to connect, but not only where extreme security is required, simply where you need to connect (i.e. the old server on your local network, where it replaced telnet+ftp). In such situations removing support for algorithms breaks the connectivity, makes backups fail, and causes lots of grief. I think that clients should not completely remove support for no-so-old algorithm but instead require an extra option like "--insecure" or something like this. Because clearly if I can't connect anymore to some of my old machines, I'll go back to telnet, which never broke accessibility in 40 years. And I do think that SSH is better than telnet, even with older keys that a neighbor could fake for $50k to intercept my connection on my local network just to send me a "you're pwned" banner when I connect...
OpenSSH 8.6 released
Posted Apr 20, 2021 7:39 UTC (Tue) by cjwatson (subscriber, #7322) [Link]
OpenSSH 8.6 released
Posted Apr 20, 2021 8:21 UTC (Tue) by Sesse (subscriber, #53779) [Link]
Unable to negotiate with <ip> port 22: no matching key exchange method found. Their offer: diffie-hellman-group-exchange-sha1,diffie-hellman-group14-sha1
I sometimes keep a machine on oldstable or oldoldstable around, so that I can have an older ssh(1) binary to SSH to stuff with…
OpenSSH 8.6 released
Posted Apr 20, 2021 9:20 UTC (Tue) by dottedmag (subscriber, #18590) [Link]
OpenSSH 8.6 released
Posted Apr 20, 2021 9:32 UTC (Tue) by Sesse (subscriber, #53779) [Link]
OpenSSH 8.6 released
Posted Apr 20, 2021 10:38 UTC (Tue) by Cyberax (✭ supporter ✭, #52523) [Link]
OpenSSH 8.6 released
Posted Apr 20, 2021 8:41 UTC (Tue) by Vipketsh (guest, #134480) [Link]
It would be great if security people today would understand that security is a function of *three* things: Confidentiality, Integrity and *Availability*. Clearly availability is being reduced here for no gain in Integrity.
OpenSSH 8.6 released
Posted Apr 20, 2021 10:14 UTC (Tue) by hkario (subscriber, #94864) [Link]
That's your opinion, not shared by wider security community.
Look for SSH Downgrade Attacks to learn why.
OpenSSH 8.6 released
Posted Apr 20, 2021 10:43 UTC (Tue) by pizza (subscriber, #46) [Link]
> Look for SSH Downgrade Attacks to learn why.
Sure, and the net result of this "improved security" is "SSH downgrade to telnet"
Mission accomplished, I guess.
OpenSSH 8.6 released
Posted Apr 20, 2021 11:04 UTC (Tue) by hkario (subscriber, #94864) [Link]
Second, you aren't secure with SSHv1, at least with telnet you're not lying to yourself that you are. So there's a chance that you'll do something about it. That is improved security: real, not apparent.
OpenSSH 8.6 released
Posted Apr 20, 2021 11:32 UTC (Tue) by pizza (subscriber, #46) [Link]
What is "real, improved" over dropping the barrier of attack from $50K to $0?
At $50K, you're only going to be vulnerable to larger criminal enterprises and nation-states that are specifically going after _you_. But at $0 you're open to every script kiddie on the internet with a copy of nmap.
Your argument is equivalent to getting rid of the front doors on houses because they're easy to open.
OpenSSH 8.6 released
Posted Apr 20, 2021 11:40 UTC (Tue) by hkario (subscriber, #94864) [Link]
OpenSSH 8.6 released
Posted Apr 22, 2021 17:39 UTC (Thu) by jschrod (subscriber, #1646) [Link]
It seems that there are a lot of ssh use cases that you haven't experienced yet, especially in the network devices realm.
OpenSSH 8.6 released
Posted Apr 20, 2021 15:03 UTC (Tue) by foom (subscriber, #14868) [Link]
It's there any chance it isn't exploitable via some well known security vulnerabilities? Quite possibly even ones which have been nicely packaged into a one-click exploit toolkit, and a may be just as easy to "login" with as an ssh client...
OpenSSH 8.6 released
Posted Apr 20, 2021 14:03 UTC (Tue) by epa (subscriber, #39769) [Link]
OpenSSH 8.6 released
Posted Apr 20, 2021 16:53 UTC (Tue) by Vipketsh (guest, #134480) [Link]
OpenSSH 8.6 released
Posted Apr 20, 2021 12:21 UTC (Tue) by pabs (subscriber, #43278) [Link]
OpenSSH 8.6 released
Posted Apr 20, 2021 16:55 UTC (Tue) by floppus (guest, #137245) [Link]
Even when it comes to standard distros, though, dropbear added support for Ed25519 and RSA+SHA-2 only very recently, so those aren't yet supported in stable OpenWRT.
OpenSSH 8.6 released
Posted Apr 22, 2021 20:30 UTC (Thu) by Sesse (subscriber, #53779) [Link]
OpenSSH 8.6 released
Posted Apr 22, 2021 20:32 UTC (Thu) by pabs (subscriber, #43278) [Link]
OpenSSH 8.6 released
Posted Apr 22, 2021 20:36 UTC (Thu) by Sesse (subscriber, #53779) [Link]
OpenSSH 8.6 released
Posted Apr 22, 2021 21:00 UTC (Thu) by pabs (subscriber, #43278) [Link]
https://wiki.debian.org/Derivatives/Census/VyOS
https://wiki.debian.org/Derivatives/Census/DANOS
https://wiki.debian.org/Derivatives/Census/CumulusLinux
https://wiki.debian.org/Derivatives/Census/OpenNetworkLinux
OpenSSH 8.6 released
Posted Apr 20, 2021 13:32 UTC (Tue) by itvirta (guest, #49997) [Link]
equipment. It wasn't too long ago I used something like 'ssh -c3des' (or even 'ssh -1') to connect to some such
relic. Per-host settings for Ciphers, Protocol, KexAlgorithms and such in '.ssh/config' also help if you need to do
that often.
The problem is downgrades that can happen automatically, within the the default-enabled settings.
(And downgrading to telnet probably doesn't fit there.)
OpenSSH 8.6 released
Posted Apr 20, 2021 18:54 UTC (Tue) by lamikr (guest, #2289) [Link]
openssl req -new -x509 -keyout ca.key -out ca.pem -days 45 -config ./ca.cnf
and then check the cipher used with command:
openssl asn1parse -in ca.key
From the output I can see that the des is still used as a cipher:
64:d=4 hl=2 l= 8 prim: OBJECT :des-ede3-cbc
Shouldn't openssl use something more secure by default?
OpenSSH 8.6 released
Posted Apr 20, 2021 19:41 UTC (Tue) by tamiko (subscriber, #115350) [Link]
It should. But this is entirely orthogonal to openssh changing it's default-enabled cipher set.
OpenSSH 8.6 released
Posted Apr 22, 2021 17:42 UTC (Thu) by jschrod (subscriber, #1646) [Link]
OpenSSH 8.6 released
Posted Apr 22, 2021 10:30 UTC (Thu) by jezuch (subscriber, #52988) [Link]
What is sad is that the designers of the SSH protocol were also denying this reality. Support for *automatic* key rotation and upgrade should have been designed into the protocol from the start. It is not, so everyone has to do it manually (or automating it themselves) and everyone suffers and security suffers even more. So, in the end, I don't really blame you for moaning.
Obviously I have a couple of decades of hindsight to benefit from so I guess it turns me into a smart-ass at this point :)
OpenSSH 8.6 released
Posted Apr 22, 2021 11:42 UTC (Thu) by pizza (subscriber, #46) [Link]
Absolutely!
I'm in a situation where I have a gerrit instance using one of these these problematic host keys (generated back in 2011), mostly hit by tools (ie git) on systems I don't control. I can't replace that problematic key with a stronger one without requiring manual intervention on every single client that hits this thing. Bleh.
OpenSSH 8.6 released
Posted Apr 22, 2021 13:59 UTC (Thu) by grawity (subscriber, #80596) [Link]
I think that clients should not completely remove support for no-so-old algorithm but instead require an extra option like "--insecure" or something like this.
I somewhat agree with this, but, fortunately, OpenSSH isn't the only SSH client for Linux. PuTTY (specifically the 'plink
' command) is actively maintained and has support for everything under the sun, from Ed448 to SUPDUP.