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Category:   Application (Generic)  >   Telnet Vendors:   [Multiple Authors/Vendors]
(Caldera Issues Fix for SCO) Telnet Daemons May Give Remote Users Root Level Access Privileges
SecurityTracker Alert ID:  1002153
SecurityTracker URL:  http://securitytracker.com/id/1002153
CVE Reference:   GENERIC-MAP-NOMATCH   (Links to External Site)
Date:  Aug 7 2001
Impact:   Execution of arbitrary code via network, Root access via network, User access via network
Fix Available:  Yes  Vendor Confirmed:  Yes  

Description:   TESO reported that many BSD-derived Telnet daemons (servers) contain a vulnerability that may allow a remote user to obtain root level access on the server.

The vulnerability is reportedly due to a buffer overflow in the telnet option handling.

The following systems are reported to be vulnerable:

BSDI 4.x default, FreeBSD [2345].x default, IRIX 6.5, Linux netkit-telnetd < 0.14, NetBSD 1.x default, OpenBSD 2.x, Solaris 2.x sparc, and "almost any other vendor's telnetd".

A remote user can send a specially formatted option string to the remote telnet server and overwrite sensitive memory, causing arbitrary code to be executed with the privileges of the telnet server (which is typically root level privileges).

Telnet options are reportedly processed by the 'telrcv' function. The results of the parsing, which are to be send back to the client, are stored in the 'netobuf' buffer. It is apparently assumed that the reply data is smaller than the buffer size, so no bounds checking is performed. By using a combination of options, especially the 'AYT' Are You There option, it is possible for a remote user to append data to the buffer. It is reported that the characters that can be written to the buffer are limited, which makes constructing a successful exploit difficult.

The report states that a working exploit has been developed for BSDI, NetBSD and FreeBSD. However, the exploit was not released.

Impact:   A remote user can execute arbitrary code on the server with the privileges of the telnet server, which is typically root level privileges.
Solution:   The vendor has released a fix for SCO Unix. See the Source Message for the vendor's advisory containing directions on how to obtain the appropriate fix.
Cause:   Boundary error
Underlying OS:  UNIX (Open UNIX-SCO)
Underlying OS Comments:  many Linux and Unix OSs are vulnerable, but not all - see the Alert text for more information

Message History:   This archive entry is a follow-up to the message listed below.
Jul 18 2001 Telnet Daemons May Give Remote Users Root Level Access Privileges



 Source Message Contents

Subject:  Security Update: [CSSA-2001-SCO.9] Open Unix 8, UnixWare 7: in.telnetd buffer overflow


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To: announce@lists.caldera.com security-announce@lists.securityportal.com bugtraq@securityfocus.com

_______________________________________________________________________________

	    Caldera International, Inc. Security Advisory

Subject:		Open Unix 8, UnixWare 7.1.1: in.telnetd buffer overflow
Advisory number: 	CSSA-2001-SCO.9
Issue date: 		2001 August 1
Cross reference:
_______________________________________________________________________________



1. Problem Description
	
	The telnet daemon /usr/sbin/in.telnetd is subject to a buffer
	overflow problem that could be used by a malicious user to
	gain unauthorized access to a system.


2. Vulnerable Versions

	Operating System	Version		Affected Files
	------------------------------------------------------------------
	UnixWare 7		All		/usr/sbin/in.telnetd
	Open Unix 8		All		/usr/sbin/in.telnetd

3. Workaround

	None.


4. UnixWare 7

  4.1 Location of Fixed Binaries

	ftp://ftp.sco.com/pub/security/unixware/sr849877/


  4.2 Verification

	md5 checksums:
	
	3870368dee25d0c957125c53c91599ee	erg711792a.Z


	md5 is available for download from

		ftp://ftp.sco.com/pub/security/tools/


  4.3 Installing Fixed Binaries

	Upgrade the affected binaries with the following commands:

	# uncompress /tmp/erg711792a.Z
	# pkgadd -d /tmp/erg711792a


5. Open Unix 8

  5.1 Location of Fixed Binaries

	ftp://ftp.sco.com/pub/security/openunix/sr849878/


  5.2 Verification

	md5 checksums:
	
	3870368dee25d0c957125c53c91599ee	erg711792a.Z


	md5 is available for download from

		ftp://ftp.sco.com/pub/security/tools/


  5.3 Installing Fixed Binaries

	Upgrade the affected binaries with the following commands:

	# uncompress /tmp/erg711792a.Z
	# pkgadd -d /tmp/erg711792a


6. References

	http://www.calderasystems.com/support/security/index.html


7. Disclaimer

	Caldera International, Inc. is not responsible for the misuse
	of any of the information we provide on our website and/or
	through our security advisories. Our advisories are a service
	to our customers intended to promote secure installation and
	use of Caldera International products.


8.Acknowledgements

	Caldera International would like to thank Sebastian
	<scut@nb.in-berlin.de> for his posting on bugtraq, and KF
	<dotslash@snosoft.com> for reporting the problem to us.
	 
___________________________________________________________________________

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