Bug 1546241 – CVE-2018-7169 shadow-utils: newgidmap allows unprivileged user to drop supplementary groups potentially allowing privilege escalation

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Bug 1546241 - (CVE-2018-7169) CVE-2018-7169 shadow-utils: newgidmap allows unprivileged user to drop supplementary groups potentially allowing privilege escalation

Summary:	CVE-2018-7169 shadow-utils: newgidmap allows unprivileged user to drop supple...

Status:	CLOSED NOTABUG

Aliases:	CVE-2018-7169

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

Priority	medium Severity medium
Target Milestone:	---
Target Release:	---
Assigned To:	Red Hat Product Security
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URL:
Whiteboard:	impact=moderate,public=20171114,repor...
Keywords:	Security

Depends On:	1546242 1546243
Blocks:	1546245
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Reported:	2018-02-16 12:27 EST by Adam Mariš
Modified:	2018-06-05 07:27 EDT (History)
CC List:	5 users (show)

See Also:
Fixed In Version:
Doc Type:	If docs needed, set a value
Doc Text:	An issue was discovered in newgidmap, in shadow-utils, that allows an unprivileged user to be placed in a user namespace where setgroups is permitted. An attacker could use this flaw to remove himself from a supplementary group, which may allow access to certain filesystem paths, if the administrator has used "group blacklisting" (e.g., chmod g-rwx) to restrict access to paths.
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Last Closed:	2018-03-01 11:48:13 EST
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Description Adam Mariš 2018-02-16 12:27:09 EST

An issue was discovered in shadow 4.5. newgidmap (in shadow-utils) is setuid and allows an unprivileged user to be placed in a user namespace where setgroups(2) is permitted. This allows an attacker to remove themselves from a supplementary group, which may allow access to certain filesystem paths if the administrator has used "group blacklisting" (e.g., chmod g-rwx) to restrict access to paths. This flaw effectively reverts a security feature in the kernel (in particular, the /proc/self/setgroups knob) to prevent this sort of privilege escalation.

Bug report:

https://bugs.launchpad.net/ubuntu/+source/shadow/+bug/1729357

Upstream patch:

https://github.com/shadow-maint/shadow/pull/97

Comment 1 Adam Mariš 2018-02-16 12:27:41 EST

Created shadow-utils tracking bugs for this issue:

Affects: fedora-all [bug 1546242]

Comment 3 Riccardo Schirone 2018-02-28 05:07:21 EST

There is an ongoing effort upstream to make newgidmap more configurable and let the administrator choose which users can use setgroups(2) in the user namespace.

https://github.com/shadow-maint/shadow/pull/99

Comment 5 Riccardo Schirone 2018-03-01 11:45:16 EST

Statement:

This issue did not affect the versions of shadow-utils as shipped with Red Hat Enterprise Linux 5, 6 and 7 as they did not provide newgidmap program.

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