Attachment 15030 Details for Bug 13851 – advisory with CVE (v5)

advisory with CVE (v5)

CVE-2019-3880-advisory-05.txt (text/plain), 3.01 KB, created by Andrew Bartlett on 2019-04-01 01:12:19 UTC

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Creator: Andrew Bartlett

Created: 2019-04-01 01:12:19 UTC

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obsolete

>===========================================================
>== Subject:     Save registry file outside share as unprivileged user
>==
>== CVE ID#:     CVE-2019-3880
>==
>== Versions:    All versions of Samba since Samba 3.2.0
>==
>== Summary:     Authenticated users with write permission
>                can trigger a symlink traversal to write
>		or detect files outside the Samba share.
>===========================================================
>
>===========
>Description
>===========
>
>Samba contains an RPC endpoint emulating the Windows registry service
>API. One of the requests, "winreg_SaveKey", is susceptible to a
>path/symlink traversal vulnerability. Unprivileged users can use it to
>create a new registry hive file anywhere they have unix permissions to
>create a new file within a Samba share. If they are able to create
>symlinks on a Samba share, they can create a new registry hive file
>anywhere they have write access, even outside a Samba share
>definition.
>
>Note - existing share restrictions such as "read only" or share ACLs
>do *not* prevent new registry hive files being written to the
>filesystem. A file may be written under any share definition wherever
>the user has unix permissions to create a file.
>
>Existing files cannot be overwritten using this vulnerability, only
>new registry hive files can be created, however the presence of
>existing files with a specific name can be detected.
>
>Samba writes or detects the file as the authenticated user, not as root.
>
>==================
>Patch Availability
>==================
>
>Patches addressing both these issues have been posted to:
>
>    http://www.samba.org/samba/security/
>
>Additionally, Samba 4.8.11, 4.9.6 and 4.10.2 have been issued as
>security releases to correct the defect.  Samba administrators are
>advised to upgrade to these releases or apply the patch as soon as
>possible.
>
>==================
>CVSSv3 calculation
>==================
>
>CVSS:3.0/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:L (6.3)
>
>==========
>Workaround
>==========
>
>If the areas of the filesystem being exported by all share definitions
>have no symlinks pointing outside the shared areas, the attacker can
>only create new files inside the shared areas.
>
>Is the server is exporting SMB1 shares, and the global parameter 'unix
>extensions = yes' is set (the default value), then an attacker can
>create symbolic links that point outside the share definitions to
>allow registry hive files to be created wherever the symlink points to
>(so long as no existing file is present).
>
>Either turn off SMB1 by setting the global parameter:
>
>'min protocol = SMB2'
>
>or if SMB1 is required turn off unix extensions by setting the global
>parameter:
>
>'unix extensions = no'
>
>in the smb.conf file.
>
>=======
>Credits
>=======
>
>Originally reported by Michael Hanselmann.
>
>Patches provided by Jeremy Allison of the Samba Team and Google.
>Advisory written by Andrew Bartlett of the Samba Team and Catalyst.
>
>==========================================================
>== Our Code, Our Bugs, Our Responsibility.
>== The Samba Team
>==========================================================

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