Hi All,
In my never ending quest to find new and annoying ways to do everything, I figured that I'd throw out the new list of fun.
1. Using pkexec makes sudo relatively pointless. Sure, it logs things, but we now effectively have two sudo subsystems and one can't really have the rules audited per my last discussion with Steve because JavaScript as a configuration language is amazing. Not sure what to do about this one but people should really be watching for it and I don't see any mention of it in the rules anywhere.
2. Systemd timers can be run in user mode and effectively make all the restrictions around cron and at pointless from what I can tell. So far, I can't figure out how to disable user space timers or 'systemctl --user' calls without completely removing 'pam_systemd' from the stack. No idea what this would break but it's probably the only solution right now (or maybe having a group-based jump stack in PAM).
3. There should probably be some sort of check to make sure that 'enable-linger' has not been set for users.
In summary, the SSG simply does not cover any of the new EL7+ capabilities very well, particularly those that replace traditional services that are already expected to be controlled. As systemd becomes more of an operating system and less of service manager, this will only get worse.
Thanks,
Trevor
Hello,
On Monday, November 26, 2018 9:18:07 AM EST Trevor Vaughan wrote:
In my never ending quest to find new and annoying ways to do everything, I figured that I'd throw out the new list of fun.
- Using pkexec makes sudo relatively pointless. Sure, it logs things,
It does not send audit events which is a big deal.
but we now effectively have two sudo subsystems and one can't really have the rules audited per my last discussion with Steve because JavaScript as a configuration language is amazing. Not sure what to do about this one but people should really be watching for it and I don't see any mention of it in the rules anywhere.
What I told the Fedora community is that the only thing that can be done is to get a SHA256 hash of the auth file and compare that during security audits. Its suboptimal but should work.
- Systemd timers can be run in user mode and effectively make all the
restrictions around cron and at pointless from what I can tell.
Cron and at can do auditing and MLS. Which is a big deal for security. Systemd has no auditing for timers nor can it do MLS. One thing to know about systemd is that they place a lot of functionality in it for minimal systems. For example if you are designing an embedded system, then systemd's functionality may be good enough such that you do not need to drag in lots of dependencies which increase the footprint. However, it is not a replacement for full fledged security solutions. For example, systemd can replace xinetd. However, it cannot do MLS nor any of the fancy blocking that xinetd can do.
So far, I can't figure out how to disable user space timers or 'systemctl --user' calls without completely removing 'pam_systemd' from the stack. No idea what this would break but it's probably the only solution right now (or maybe having a group-based jump stack in PAM).
If it cannot be disabled, then it must be auditable. I'd say a bz may need to be opened on this.
-Steve
- There should probably be some sort of check to make sure that
'enable-linger' has not been set for users.
In summary, the SSG simply does not cover any of the new EL7+ capabilities very well, particularly those that replace traditional services that are already expected to be controlled. As systemd becomes more of an operating system and less of service manager, this will only get worse.
Thanks,
Trevor
Hi Steve,
On Mon, Nov 26, 2018 at 9:41 AM Steve Grubb sgrubb@redhat.com wrote:
Hello,
On Monday, November 26, 2018 9:18:07 AM EST Trevor Vaughan wrote:
In my never ending quest to find new and annoying ways to do everything,
I
figured that I'd throw out the new list of fun.
- Using pkexec makes sudo relatively pointless. Sure, it logs things,
It does not send audit events which is a big deal.
I had no idea about this. That's super fun. It logs to syslog but having it jump the audit chain is fun.
but we now effectively have two sudo subsystems and one can't really have the rules audited per my last discussion with Steve because JavaScript
as a
configuration language is amazing. Not sure what to do about this one but people should really be watching for it and I don't see any mention of it in the rules anywhere.
What I told the Fedora community is that the only thing that can be done is to get a SHA256 hash of the auth file and compare that during security audits. Its suboptimal but should work.
Unfortunately, it only works if you never add or modify anything else in that space. That means RPMs or anything else are going to have to be really carefully audited and, since it's JavaScript, you can literally embed obfuscated stuff somewhere else on the OS and call it a day. Super exciting.
Currently, I'm going with a puppet based authoritative management and purge but I'm not sure how you make that generic.
- Systemd timers can be run in user mode and effectively make all the
restrictions around cron and at pointless from what I can tell.
Cron and at can do auditing and MLS. Which is a big deal for security. Systemd has no auditing for timers nor can it do MLS. One thing to know about systemd is that they place a lot of functionality in it for minimal systems. For example if you are designing an embedded system, then systemd's functionality may be good enough such that you do not need to drag in lots of dependencies which increase the footprint. However, it is not a replacement for full fledged security solutions. For example, systemd can replace xinetd. However, it cannot do MLS nor any of the fancy blocking that xinetd can do.
So, it sounds like systemd needs to be updated with MLS/SELinux support or it needs to be able to run in "this isn't a minimial system so stop trying to be helpful" mode. In the mean time, shouldn't the SSG have rules to disable all of the shenanigans that replace better OS services. Unfortunately, I think that you may be one of the few people that can actually enumerate these without a bunch of dumpster diving.
So far, I can't figure out how to disable user space timers or 'systemctl --user' calls without completely removing 'pam_systemd' from the stack. No idea what this would break but it's probably the only solution right now (or maybe having a group-based jump stack in PAM).
If it cannot be disabled, then it must be auditable. I'd say a bz may need to be opened on this.
Well, is there a problem with jumping over `pam_systemd` except for specific users? I simply don't know what this would break. If that works, then we can add that to the SSG. If not, yeah, that could be a problem.
-Steve
- There should probably be some sort of check to make sure that
'enable-linger' has not been set for users.
I did a quick dig on this one and it looks like auditing /var/lib/systemd/linger for files should work fine and should be simple to implement.
In summary, the SSG simply does not cover any of the new EL7+
capabilities
very well, particularly those that replace traditional services that are already expected to be controlled. As systemd becomes more of an
operating
system and less of service manager, this will only get worse.
Thanks,
Trevor
On a related note to pkexec, anyone know how to mitigate this?
https://thehackernews.com/2018/12/linux-user-privilege-policykit.html
Thanks,
Trevor
On Mon, Nov 26, 2018 at 10:03 AM Trevor Vaughan tvaughan@onyxpoint.com wrote:
Hi Steve,
On Mon, Nov 26, 2018 at 9:41 AM Steve Grubb sgrubb@redhat.com wrote:
Hello,
On Monday, November 26, 2018 9:18:07 AM EST Trevor Vaughan wrote:
In my never ending quest to find new and annoying ways to do
everything, I
figured that I'd throw out the new list of fun.
- Using pkexec makes sudo relatively pointless. Sure, it logs things,
It does not send audit events which is a big deal.
I had no idea about this. That's super fun. It logs to syslog but having it jump the audit chain is fun.
but we now effectively have two sudo subsystems and one can't really
have
the rules audited per my last discussion with Steve because JavaScript
as a
configuration language is amazing. Not sure what to do about this one
but
people should really be watching for it and I don't see any mention of
it
in the rules anywhere.
What I told the Fedora community is that the only thing that can be done is to get a SHA256 hash of the auth file and compare that during security audits. Its suboptimal but should work.
Unfortunately, it only works if you never add or modify anything else in that space. That means RPMs or anything else are going to have to be really carefully audited and, since it's JavaScript, you can literally embed obfuscated stuff somewhere else on the OS and call it a day. Super exciting.
Currently, I'm going with a puppet based authoritative management and purge but I'm not sure how you make that generic.
- Systemd timers can be run in user mode and effectively make all the
restrictions around cron and at pointless from what I can tell.
Cron and at can do auditing and MLS. Which is a big deal for security. Systemd has no auditing for timers nor can it do MLS. One thing to know about systemd is that they place a lot of functionality in it for minimal systems. For example if you are designing an embedded system, then systemd's functionality may be good enough such that you do not need to drag in lots of dependencies which increase the footprint. However, it is not a replacement for full fledged security solutions. For example, systemd can replace xinetd. However, it cannot do MLS nor any of the fancy blocking that xinetd can do.
So, it sounds like systemd needs to be updated with MLS/SELinux support or it needs to be able to run in "this isn't a minimial system so stop trying to be helpful" mode. In the mean time, shouldn't the SSG have rules to disable all of the shenanigans that replace better OS services. Unfortunately, I think that you may be one of the few people that can actually enumerate these without a bunch of dumpster diving.
So far, I can't figure out how to disable user space timers or 'systemctl --user' calls without completely removing 'pam_systemd' from the stack. No idea what this would break but it's probably the only solution right now (or maybe having a group-based jump stack in PAM).
If it cannot be disabled, then it must be auditable. I'd say a bz may need to be opened on this.
Well, is there a problem with jumping over `pam_systemd` except for specific users? I simply don't know what this would break. If that works, then we can add that to the SSG. If not, yeah, that could be a problem.
-Steve
- There should probably be some sort of check to make sure that
'enable-linger' has not been set for users.
I did a quick dig on this one and it looks like auditing /var/lib/systemd/linger for files should work fine and should be simple to implement.
In summary, the SSG simply does not cover any of the new EL7+
capabilities
very well, particularly those that replace traditional services that are already expected to be controlled. As systemd becomes more of an
operating
system and less of service manager, this will only get worse.
Thanks,
Trevor
-- Trevor Vaughan Vice President, Onyx Point, Inc (410) 541-6699 x788
-- This account not approved for unencrypted proprietary information --
On 12/6/18 2:13 PM, Trevor Vaughan wrote:
On a related note to pkexec, anyone know how to mitigate this?
https://thehackernews.com/2018/12/linux-user-privilege-policykit.html
https://access.redhat.com/security/cve/cve-2018-19788
"Do not allow negative UIDs or UIDs greater than 2147483646."
....... which is weird, since patches were upstream: - https://gitlab.freedesktop.org/zbyszek/polkit/commit/fbaab32cb4ed9ed5f1e3eea... - https://gitlab.freedesktop.org/zbyszek/polkit/commit/7c8c3abdedbb991a69bc5f1...
I'll ask around on the RHEL product security team to see what's up.
On 12/6/18 2:18 PM, Shawn Wells wrote:
On 12/6/18 2:13 PM, Trevor Vaughan wrote:
On a related note to pkexec, anyone know how to mitigate this?
https://thehackernews.com/2018/12/linux-user-privilege-policykit.html
https://access.redhat.com/security/cve/cve-2018-19788
"Do not allow negative UIDs or UIDs greater than 2147483646."
....... which is weird, since patches were upstream:
https://gitlab.freedesktop.org/zbyszek/polkit/commit/fbaab32cb4ed9ed5f1e3eea...
https://gitlab.freedesktop.org/zbyszek/polkit/commit/7c8c3abdedbb991a69bc5f1...
I'll ask around on the RHEL product security team to see what's up.
If anyone wants to follow along: https://bugzilla.redhat.com/show_bug.cgi?id=1655925
On 12/6/18 2:20 PM, Shawn Wells wrote:
On 12/6/18 2:18 PM, Shawn Wells wrote:
On 12/6/18 2:13 PM, Trevor Vaughan wrote:
On a related note to pkexec, anyone know how to mitigate this?
https://thehackernews.com/2018/12/linux-user-privilege-policykit.html
https://access.redhat.com/security/cve/cve-2018-19788
"Do not allow negative UIDs or UIDs greater than 2147483646."
....... which is weird, since patches were upstream:
https://gitlab.freedesktop.org/zbyszek/polkit/commit/fbaab32cb4ed9ed5f1e3eea...
https://gitlab.freedesktop.org/zbyszek/polkit/commit/7c8c3abdedbb991a69bc5f1...
I'll ask around on the RHEL product security team to see what's up.
If anyone wants to follow along: https://bugzilla.redhat.com/show_bug.cgi?id=1655925
update: RHEL7 patch currently going through QA and should be released shortly.
Shawn,
While this fixes the symptom, I think that this is actually a systemd bug as well. Libvirt handles incorrect UID entries correctly.
https://bugzilla.redhat.com/show_bug.cgi?id=1657021
The error handling in the authorization stack probably needs to be analyzed.
On Thu, Dec 6, 2018 at 2:23 PM Shawn Wells shawn@redhat.com wrote:
On 12/6/18 2:20 PM, Shawn Wells wrote:
On 12/6/18 2:18 PM, Shawn Wells wrote:
On 12/6/18 2:13 PM, Trevor Vaughan wrote:
On a related note to pkexec, anyone know how to mitigate this?
https://thehackernews.com/2018/12/linux-user-privilege-policykit.html
https://access.redhat.com/security/cve/cve-2018-19788
"Do not allow negative UIDs or UIDs greater than 2147483646."
....... which is weird, since patches were upstream:
https://gitlab.freedesktop.org/zbyszek/polkit/commit/fbaab32cb4ed9ed5f1e3eea...
https://gitlab.freedesktop.org/zbyszek/polkit/commit/7c8c3abdedbb991a69bc5f1...
I'll ask around on the RHEL product security team to see what's up.
If anyone wants to follow along: https://bugzilla.redhat.com/show_bug.cgi?id=1655925
update: RHEL7 patch currently going through QA and should be released shortly. _______________________________________________ scap-security-guide mailing list -- scap-security-guide@lists.fedorahosted.org To unsubscribe send an email to scap-security-guide-leave@lists.fedorahosted.org Fedora Code of Conduct: https://getfedora.org/code-of-conduct.html List Guidelines: https://fedoraproject.org/wiki/Mailing_list_guidelines List Archives: https://lists.fedorahosted.org/archives/list/scap-security-guide@lists.fedor...
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