Date: Sun, 12 Sep 2021 10:40:49 -0400 From: Karl Denninger <karl@denninger.net> To: freebsd-security@freebsd.org Subject: Re: Important note for future FreeBSD base system OpenSSH update Message-ID: <2bb56783-2727-9bea-7810-58969d91c00f@denninger.net> In-Reply-To: <8169A4A8-B8D1-4265-87C8-74ED4D34FBC8@fasel.at> References: <CAPyFy2A390kS_C3g=Y9QhQcJ06z_FKUxXsNvi9g2CdWF24pukg@mail.gmail.com> <CAPyFy2B04b0GtWoHFQwxht5vK4_cnApPXpDLXU%2BRvcR=2L9YxA@mail.gmail.com> <CAPyFy2Aw8Z3ngiM8YHApjjPRLZVC5MCN8TRQkh6pj2fSeM1zqw@mail.gmail.com> <8169A4A8-B8D1-4265-87C8-74ED4D34FBC8@fasel.at>
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This is a cryptographically signed message in MIME format. --------------ms070404000009040207020201 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: quoted-printable On 9/12/2021 10:02, Markus Falb wrote: >> On 09.09.2021, at 20:01, Ed Maste <emaste@freebsd.org> wrote: >> >> OpenSSH will disable the ssh-rsa signature scheme by default in the >> next release. >> >> ... >> >> 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=3D-ssh-rsa user@host > FWIW, some of us may already have dealt with that. > FIPS enabled RedHat Enterprise Linux (and probably other FIPS enabled > systems) means effectively no ssh-rsa signature available in the sshd. > I had that situation at the beginning of the year. > > As mentioned, ssh-rsa signature algorithm will stop working, but > that does not automatically imply that every RSA key must be > changed to something other. The signature algorithm is not a > property that is inherent to the key. > > That said, existing RSA keys were working fine for me (my openssh > client was rsa-sha2-256 and rsa-sha2-512 capable) but when I tested > with some popular windows clients (filezilla, putty) it failed > (apparently no rsa-sha2 algorithms available). > > I found it interesting that mentioned clients were ecdsa > capable but did not support sha2 signatures with RSA keys. > Maybe the situation changed in the meantime to the better. > > There are 3 scenarios: > > 1. both sides support rsa-sha2 signatures -> RSA keys still working > > 2. one side does not support sha2 signatures but does support other > key types -> you can change key type > > 3. one side does not support sha2 and no other key type -> you loose > > A prominent candidate for 3. would be Cisco IOS This has come up before with web browsers and is a serious PITA when=20 there is no override available for those who need it on a targeted,=20 specific basis. I have in the field a BUNCH of "smart" rack power strips that have this=20 problem; their management firmware does NOT support more-modern cipher=20 sets and SSL requirements.=C2=A0 I get it, those older SSL versions are=20 insecure and we know it.=C2=A0 But when the browser people all decided to= =20 kill the ability to connect to such servers with no override (that is,=20 don't warn, DENY with no option to get around it) all of a sudden=20 logging into those strips to change (for example) the name of a socket,=20 the alarm limits and similar became literally impossible.=C2=A0 Contactin= g=20 the manufacturer resulted in a middle finger back; "nope, we're not=20 releasing new firmware for that."=C2=A0 I've seen the same thing with som= e=20 older OOB management interfaces on server boards; they won't take an=20 acceptably-long (by modern standards) HTTPS server key, and thus, same=20 problem and same answer from the manufacturer.=C2=A0 These are=20 perfectly-serviceable devices in their application and quite-expensive=20 to replace when there's nothing wrong with them. On the server boards by = now they've all been retired as people decided the better power budget=20 and performance levels made changing them (and re-purchasing the RAM=20 that went on them, which for larger servers is a non-trivial part of the = total expense) a reasonable proposition.=C2=A0 This of course is not true= for=20 a smart power strip in the rack and makes both monitoring of energy and=20 remote-hard-power-cycle available without a physical site visit or=20 remote hands. In the case of the power strips the "answer" was one of the prepackaged, = self-contained old "portable" versions of FireFox which complains but=20 the alert can be clicked through.=C2=A0 I recognize that exposing those=20 devices to the Internet is unsafe but have never trusted that anyway;=20 they're behind a gateway box with no port hole punch and if I'm VPN'd in = then it's not possible for a random person to screw with it. It would be sad indeed if the only answer here is "load up a partition=20 with an older copy of FreeBSD on some device and use that."=C2=A0 Can we = avoid that being the answer, as it became with the browser issues? --=20 Karl Denninger karl@denninger.net <mailto:karl@denninger.net> /The Market Ticker/ /[S/MIME encrypted email preferred]/ --------------ms070404000009040207020201 Content-Type: application/pkcs7-signature; name="smime.p7s" Content-Transfer-Encoding: base64 Content-Disposition: attachment; filename="smime.p7s" Content-Description: S/MIME Cryptographic Signature MIAGCSqGSIb3DQEHAqCAMIACAQExDzANBglghkgBZQMEAgMFADCABgkqhkiG9w0BBwEAAKCC DdgwggagMIIEiKADAgECAhMA5EiKghDOXrvfxYxjITXYDdhIMA0GCSqGSIb3DQEBCwUAMIGL MQswCQYDVQQGEwJVUzEQMA4GA1UECAwHRmxvcmlkYTESMBAGA1UEBwwJTmljZXZpbGxlMRkw FwYDVQQKDBBDdWRhIFN5c3RlbXMgTExDMRgwFgYDVQQLDA9DdWRhIFN5c3RlbXMgQ0ExITAf BgNVBAMMGEN1ZGEgU3lzdGVtcyBMTEMgMjAxNyBDQTAeFw0xNzA4MTcxNjQyMTdaFw0yNzA4 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