reply inline On 7/11/2022 4:30 AM, Stephan Wonczak ([email protected]) wrote:
Hi Jeffrey, Thanks for having a look at the problem.However, I obviously did not do a very good job detailing exactly what we did ... so here's my next try. Warning: It is going to be lengthy :-)First off: We do not use SSSD. And we would like to keep it that way, since it caused various massive problems in the past.On RHEL-7, everything works perfectly. We are using the RedHat-supplied RPM of pam_krb5: pam_krb5-2.4.8-6.el7.x86_64
The version of pam_krb5 is not the only variable that matters. As I mentioned in my earlier replies pam_krb5-2.4.8-6.el7 does not include support for rxkad-kdf which is required in order to make use of Kerberos encryption types other than des-cbc-crc for example aes256-cts-hmac-sha1-96. Without that functonality pam_krb5 only works with Kerberos v5 service tickets whose session keys are des-cbc-crc.
<working output from rhel7 removed>
We then took the source PRM: pam_krb5-2.4.8-6.el7.src.rpm and did a rebuild on a RHEL-8-Machine. This worked without any errors.However, when we try to use this to get a token, this happens: ...Jul 8 15:14:57 kicktest.rrz.uni-koeln.de sshd[2204130]: pam_krb5[2204130]: error obtaining credentials for 'afs/[email protected]' (enctype=1) on behalf of '[email protected]': No credentials found with supported encryption types Jul 8 15:14:57 kicktest.rrz.uni-koeln.de sshd[2204130]: pam_krb5[2204130]: error obtaining credentials for 'afs/[email protected]' (enctype=2) on behalf of '[email protected]': No credentials found with supported encryption types Jul 8 15:14:57 kicktest.rrz.uni-koeln.de sshd[2204130]: pam_krb5[2204130]: error obtaining credentials for 'afs/[email protected]' (enctype=3) on behalf of '[email protected]': No credentials found with supported encryption types Jul 8 15:14:57 kicktest.rrz.uni-koeln.de sshd[2204130]: pam_krb5[2204130]: attempting to obtain tokens for "rrz.uni-koeln.de" ("[email protected]") Jul 8 15:14:57 kicktest.rrz.uni-koeln.de sshd[2204130]: pam_krb5[2204130]: error obtaining credentials for '[email protected]' (enctype=1) on behalf of '[email protected]': No credentials found with supported encryption types Jul 8 15:14:57 kicktest.rrz.uni-koeln.de sshd[2204130]: pam_krb5[2204130]: error obtaining credentials for '[email protected]' (enctype=2) on behalf of '[email protected]': No credentials found with supported encryption types Jul 8 15:14:57 kicktest.rrz.uni-koeln.de sshd[2204130]: pam_krb5[2204130]: error obtaining credentials for '[email protected]' (enctype=3) on behalf of '[email protected]': No credentials found with supported encryption types...
ETYPE_DES_CBC_CRC(1) ETYPE_DES_CBC_MD4(2) ETYPE_DES_CBC_MD5(3)The pam_krb5 from rhel7 only knows how to request tickets with DES encryption types. It assumes that OpenAFS cannot support anything else because it does not have the rxkad-kdf functionality that was added to pam_krb5 post-rhel7 (Jan 4, 2016):
https://github.com/frozencemetery/pam_krb5/commit/3be27655bf9d2520e776ef22ba6bb9486005fff1
To reiterate: We get both kerberos ticket and AFS-Token on RHEL-7. On RHEL-8, we still get a valid kerberos ticket, but getting the AFS-Token fails. It -is- possible, however, to get a valid AFS-Token by klog.krb5. So -in principle- everything is in place to have this done by pam_afs. The problem is: I have no way to determine why it is complaining about "no supported encryption types" when other tools have no problems at all!
The answer to this is simple. The krb5 libraries included in rhel7 support DES encryption types. The krb5 libraries included with rhel8 do not. As a result, a pam_krb5 that supports rxkad-kdf is required.
I hope the vno 4 des-cbc-crc key is not present on any of the rrz.uni-koeln.de servers. If it is, the servers are still vulnerable toAdditional infO. Yes, we did rekey our AFS-cell quite a while ago, and our afs-Principal has two keys:kadmin.local: getprinc afs/rrz.uni-koeln.de Principal: afs/[email protected] <snip> Anzahl der Schlüssel: 2 Key: vno 5, aes256-cts-hmac-sha1-96 Key: vno 4, des-cbc-crc MKey: vno 1 Attribute: REQUIRES_PRE_AUTH Richtlinie: [keins]
OPENAFS-SA-2013-003 - Brute force DES attack permits compromise of AFS cell
http://www.openafs.org/pages/security/#OPENAFS-SA-2013-003
Like I said before, I looked at the sources of our version of pam_krb5, and the part where it is failing starts at line 775 inside the function "minikafs_5log_with_principal" (I'll attach the minikafs.c to this mail for reference)
This version of minikafs.c does not support rxkad-kdf.
Deploy a version of pam_krb5 which contains the required rxkad-kdf functionality. The version from rhel7 cannot be used successfully with the MIT Kerberos included with RHEL8 and later releases.If you or anyone else has any ideas how to tackle the problem, any help would be greatly appreciated.
Jeffrey Altman
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