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From: Erik Parker erik.parker@digitaldefense.net To: bugtraq@securityfocus.com Subject: [DDI-1013] Buffer Overflow in Samba allows remote root compromise Date: 07 Apr 2003 07:45:16 +0000

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|------------------------------------------------------------------------------| Digital Defense Inc. Security Advisory DDI-1013 labs@digitaldefense.net http://www.digitaldefense.net/ |------------------------------------------------------------------------------|

Synopsis : Buffer Overflow in Samba allows remote root compromise Package : Samba, Samba-TNG Type : Remote Root Compromise Issue date : 04-07-2003 Versions Affected : < Samba 2.2.8a, <= Samba 2.0.10, < Samba-TNG 0.3.2 Not Affected : Samba 3.0 Alpha Versions, CVS Versions of Samba-TNG CVE Id : CAN-2003-0201

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o Product description: Samba is an Open Source/Free Software suite that provides seamless file and print services to SMB/CIFS clients. Samba-TNG was originally a fork off of the Samba source tree, and aims at being a substitute for a Windows NT domain controller.

o Problem description: An anonymous user can gain remote root access due to a buffer overflow caused by a StrnCpy() into a char array (fname) using a non-constant length (namelen).

StrnCpy(fname,pname,namelen); /* Line 252 of smbd/trans2.c */

In the call_trans2open function in trans2.c, the Samba StrnCpy function copies pname into fname using namelen. The variable namelen is assigned the value of strlen(pname)+1, which causes the overflow.

The variable 'fname' is a _typedef_ pstring, which is a char with a size of 1024. If pname is greater than 1024, you can overwrite almost anything you want past the 1024th byte that fits inside of sizeof(pname), or the value returned by SVAL(inbuf,smbd_tpscnt) in function reply_trans2(), which should be around 2000 bytes.

The Common Vulnerabilities and Exposures (CVE) project has assigned the name CAN-2003-0201 to this issue. This is a candidate for inclusion in the CVE list (http://cve.mitre.org), which standardizes names for security problems.

o Testing Environment: Tested against source compiles and binary packages of Samba from version 2.2.5 to 2.2.8 on the following x86 platforms:

Redhat Linux 7.1, 7.3, 8.0 Gentoo Linux 1.4-rc3 SuSe Linux 7.3 FreeBSD 4.6, 4.8, 5.0 Solaris 9

o Solutions and Workarounds: Upgrading to the latest version of Samba or Samba-TNG is the recommended solution to this vulnerability. Samba version 2.2.8a, and Samba-TNG version 0.3.2 are not vulnerable. There will be no new releases for the 2.0 line of Samba code. The only fix for Samba 2.0 is to apply the patches that Samba is providing.

A workaround in the current source code for this specific vulnerability would be to modify the StrnCpy line found at line 250 in smbd/trans2.c in the Samba 2.2.8 source code:

-StrnCpy(fname,pname,namelen); +StrnCpy(fname,pname,MIN(namelen, sizeof(fname)-1));

As a result of this vulnerability being identified at least three others have also been found by the Samba team after reviewing similar usages in the source tree. One is a static overflow and the other two are heap overflows. Applying the fix above will only protect against the specific problem identified in this advisory. To fully protect yourself, you must apply the patches from Samba, or upgrade to 2.2.8a.

Samba is available for download from: http://www.samba.org/ Samba-TNG is available for download from: http://www.samba-tng.org/

o Exploit: An exploit named trans2root.pl has been posted on the Digital Defense, Inc. website. A quick udp based based scanner named nmbping.pl has also been posted to assist you in identifying Samba servers on your network. Both are available for download from the following URL:

http://www.digitaldefense.net/labs/securitytools.html

This exploit works against all distributions listed in the testing environment section. Usage is as follows:

trans2root.pl <options> -t <target type> -H <your ip> -h <target ip>

This exploit should work against all x86 Linux, Solaris, and FreeBSD hosts running the 2.2.x branch of Samba. Hosts with a non-executable stack are not vulnerable to this particular exploit. The exploit will cause the target host to connect back to the host running the exploit and spawn a root shell on the defined port (default is 1981).

The scanner is very easy to use, and should detect and identify Samba and Windows SMB services. Usage is as follows:

nmbping.pl <network/cidr>

o Forced Release: This vulnerability is being actively exploited in the wild. Digital Defense, Inc. discovered this bug by analyzing a packet capture of an attack against a host running Samba 2.2.8. The attack captured was performed on April 1st, 2003. Samba users are urged to check their Samba servers for signs of compromise. Samba and Digital Defense, Inc. decided to release their advisories before all vendors had a chance to update their packages due to this vulnerability being actively exploited.

o Revision History: 04-07-2003 Initial public release

Latest revision available at: http://www.digitaldefense.net/labs/advisories.html

o Vendor Contact Information: 04-03-2003 security@samba.org notified 04-03-2003 elrond@samba-tng.org notified. 04-03-2003 Samba Team responds via telephone, acknowledges vulnerability 04-03-2003 Elrond of Samba-TNG responds and acknowledges vulnerability 04-04-2003 Samba Team notifies vendorsec mailing list 04-07-2003 Initial public release

o Thanks to: Elrond of Samba-TNG, The Samba Security Team, and everyone on the Digital Defense Inc., SECOPS team.