Bug 613712 (CVE-2017-2619) – <net-fs/samba-{4.5.7,4.6.1}: symlink race permits opening files outside share directory (CVE-2017-2619)

• Product: Gentoo Security
• Status: RESOLVED FIXED

[Description Frank Krömmelbein 2017-03-24 08:48:28 UTC]

https://www.samba.org/samba/security/CVE-2017-2619.html

Subject:     Symlink race allows access outside share definition.
CVE ID#:     CVE-2017-2619
Versions:    All versions of Samba prior to 4.6.1, 4.5.7, 4.4.12
Summary:     A time-of-check, time-of-use race condition
		can allow clients to access non-exported parts
		of the file system via symlinks.

All versions of Samba prior to 4.6.1, 4.5.7, 4.4.12 are vulnerable to
a malicious client using a symlink race to allow access to areas of
the server file system not exported under the share definition.

Samba uses the realpath() system call to ensure when a client requests
access to a pathname that it is under the exported share path on the
server file system.

Clients that have write access to the exported part of the file system
via SMB1 unix extensions or NFS to create symlinks can race the server
by renaming a realpath() checked path and then creating a symlink. If
the client wins the race it can cause the server to access the new
symlink target after the exported share path check has been done. This
new symlink target can point to anywhere on the server file system.

This is a difficult race to win, but theoretically possible. Note that
the proof of concept code supplied wins the race reliably only when
the server is slowed down using the strace utility running on the
server. Exploitation of this bug has not been seen in the wild.

[Comment 1 Lars Wendler (Polynomial-C) (RETIRED) 2017-03-24 09:01:00 UTC]

commit 49b774319eec93601a9ad48bbad32f6db0bbbd84
Author: Lars Wendler <[e-mail]>
Date:   Fri Mar 24 09:56:00 2017

    net-fs/samba: Bump to versions 4.5.7 and 4.6.1

    Package-Manager: Portage-2.3.5, Repoman-2.3.2

[Comment 2 Thomas Deutschmann (RETIRED) 2017-06-04 21:48:15 UTC]

Cleanup moved to bug 619516.