Bug 1571094 – CVE-2018-1113 setup: nologin listed in /etc/shells violates security expectations

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Bug 1571094 - (CVE-2018-1113) CVE-2018-1113 setup: nologin listed in /etc/shells violates security expectations

Summary:	CVE-2018-1113 setup: nologin listed in /etc/shells violates security expectat...

Status:	NEW

Aliases:	CVE-2018-1113

Product:	Security Response
Classification:	Other
Component:	vulnerability (Show other bugs)
Sub Component:
Version:	unspecified
Hardware:	All Linux

Priority	low Severity low
Target Milestone:	---
Target Release:	---
Assigned To:	Red Hat Product Security
QA Contact:
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URL:
Whiteboard:	impact=low,public=20180424,reported=2...
Keywords:	Security

Depends On:	1571102 1571105 1378893 1571103 1571104
Blocks:	1566628
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Reported:	2018-04-24 02:03 EDT by Doran Moppert
Modified:	2018-10-30 03:53 EDT (History)
CC List:	3 users (show)

See Also:
Fixed In Version:	setup 2.11.4-1.fc28
Doc Type:	If docs needed, set a value
Doc Text:	Setup in Fedora and Red Hat Enterprise Linux added /sbin/nologin and /usr/sbin/nologin to /etc/shells. This violates security assumptions made by pam_shells and some daemons which allow access based on a user's shell being listed in /etc/shells. Under some circumstances, users which had their shell changed to /sbin/nologin could still access the system.
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RHEL 7.3 requirements from Atomic Host:
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External Trackers
Tracker	ID	Priority	Status	Summary	Last Updated
Red Hat Product Errata	RHSA-2018:3249	None	None	None	2018-10-30 03:53 EDT

Groups: None (edit)

Description Doran Moppert 2018-04-24 02:03:33 EDT

setup in Fedora and Red Hat Enterprise Linux added /sbin/nologin and /usr/sbin/nologin to /etc/shells. This violates security assumptions made by pam_shells and some daemons which allow access based on a user's shell being listed in /etc/shells.  Under some circumstances, users which had their shell changed to /sbin/nologin could still access the system.

Note that SELinux and gdm (and probably others) have special-case workarounds for this issue.

Fedora bug:  https://bugzilla.redhat.com/show_bug.cgi?id=1378893

Prior discussions:

 - https://lists.fedoraproject.org/archives/list/devel@lists.fedoraproject.org/thread/UCUWTT63JS72R7ROFE46ZVUZLFN3K2MZ/#UCUWTT63JS72R7ROFE46ZVUZLFN3K2MZ
 - https://www.redhat.com/archives/fedora-maintainers/2007-May/msg00887.html

Comment 1 Doran Moppert 2018-04-24 02:15:20 EDT

Created setup tracking bugs for this issue:

Affects: fedora-all [bug 1571103]

Comment 4 Doran Moppert 2018-06-19 23:06:18 EDT

Statement:

Preventing a user from accessing the system without deleting their account is not a simple matter. For utmost security, the account should be deleted. Short of this, we recommend a three-pronged approach:
 * change the user's login shell to a harmless command that is not in "/etc/shells" (for example "/bin/false") to prevent commands being run on their behalf
 * lock the user's password with "usermod -L" to prevent authentication with pam services
 * prevent access to the user's home directory with "chmod 0" or "chown root" and "chmod 700" to prevent authentication with ssh keys etc

Comment 5 errata-xmlrpc 2018-10-30 03:53:13 EDT

This issue has been addressed in the following products:

  Red Hat Enterprise Linux 7

Via RHSA-2018:3249 https://access.redhat.com/errata/RHSA-2018:3249

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