Bug 1233043 (CVE-2015-3245)

Summary:	CVE-2015-3245 libuser: does not filter newline characters in the GECOS field
Product:	[Other] Security Response	Reporter:	Huzaifa S. Sidhpurwala <huzaifas>
Component:	vulnerability	Assignee:	Red Hat Product Security <security-response-team>
Status:	CLOSED ERRATA	QA Contact:
Severity:	medium	Docs Contact:
Priority:	medium
Version:	unspecified	CC:	dgross, fweimer, jrusnack, mitr, sardella, security-response-team
Target Milestone:	---	Keywords:	Security
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	Bug Fix
Doc Text:	It was found that libuser, as used by the chfn userhelper functionality, did not properly filter out newline characters in GECOS fields. A local, authenticated user could use this flaw to corrupt the /etc/passwd file, resulting in a denial-of-service on the system.	Story Points:	---
Clone Of:		Environment:
Last Closed:	2015-07-29 07:17:38 UTC	Type:	---
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:
Bug Depends On:	1235517, 1235518, 1235519, 1235520, 1246225
Bug Blocks:	1233055

Description Huzaifa S. Sidhpurwala 2015-06-18 06:50:27 UTC

It was found that libuser, as used in the chfn userhelper functionality, does not properly filter out newline characters, which allows an authenticated local attacker to corrupt the /etc/passwd file and cause denial-of-service against the system.

Acknowledgements:

Red Hat would like to thank Qualys for reporting this issue.

Comment 4 Florian Weimer 2015-07-23 12:09:28 UTC

This vulnerability is addressed by additional checks on GECOS field contents within the libuser library, and not in the userhelper program in the usermode package.  This change will also protect other applications which use libuser.

Comment 5 Florian Weimer 2015-07-23 12:56:38 UTC

Mitigation:

Add pam_warn and pam_deny rules to /etc/pam.d/chfn and /etc/pam.d/chsh to prevent non-root users from using this functionality.  With these edits, the files should contain:

#%PAM-1.0
auth       sufficient   pam_rootok.so
auth required pam_warn.so
auth required pam_deny.so
auth       include      system-auth
account    include      system-auth
password   include      system-auth
session    include      system-auth

Afterwards, attempts by unprivileged users to use chfn and chsh (and the respective functionality in the userhelper program) will fail, and will be logged (by default in /var/log/secure).

Comment 6 Martin Prpič 2015-07-23 12:57:37 UTC

External References:

https://access.redhat.com/articles/1537873

Comment 7 errata-xmlrpc 2015-07-23 18:01:48 UTC

This issue has been addressed in the following products:

  Red Hat Enterprise Linux 6

Via RHSA-2015:1482 https://rhn.redhat.com/errata/RHSA-2015-1482.html

Comment 8 Florian Weimer 2015-07-23 18:11:58 UTC

Created libuser tracking bugs for this issue:

Affects: fedora-all [bug 1246225]

Comment 9 errata-xmlrpc 2015-07-23 20:45:33 UTC

This issue has been addressed in the following products:

  Red Hat Enterprise Linux 7

Via RHSA-2015:1483 https://rhn.redhat.com/errata/RHSA-2015-1483.html

Comment 10 Florian Weimer 2015-07-29 07:07:09 UTC

Statement:

Red Hat Enterprise Linux 5 is now in Production 3 Phase of the support and maintenance life cycle. This vulnerability has been rated as having Moderate security impact and is not currently planned to be addressed in future updates. For additional information, refer to the Red Hat Enterprise Linux Life Cycle: https://access.redhat.com/support/policy/updates/errata/.

Comment 11 Fedora Update System 2015-07-30 13:55:12 UTC

libuser-0.62-1.fc22 has been pushed to the Fedora 22 stable repository.  If problems still persist, please make note of it in this bug report.

Comment 12 Fedora Update System 2015-08-03 04:30:50 UTC

libuser-0.62-1.fc21 has been pushed to the Fedora 21 stable repository.  If problems still persist, please make note of it in this bug report.