Last revised: September 23, 1997
Updated Copyright statement
A complete revision history is at the end of this file. This advisory supersedes CA-91.01a and CA-91.13.
There are vulnerabilities in some versions of /bin/mail. Section III below provides vendor-specific information and an alternative to /bin/mail.
We will update this advisory as we receive additional information. Please check advisory files regularly for updates that relate to your site.
I. DescriptionSome versions of /bin/mail based on BSD 4.3 UNIX are vulnerable because of timing windows in the way /bin/mail uses publicly writable directories.
II. ImpactLocal users (users that have an account on the system) can create or modify root-owned files on the system and can thereby gain unauthorized root access.
III. SolutionsEither install a patch from your vendor or replace /bin/mail with mail.local.
A. Obtain the appropriate patch from your vendor and install it according to the instructions included with the patch.
Below is a summary of the vendors listed in Appendix A of this advisory and the information they have provided. If your vendor's name is not on this list, please contact the vendor directly.
|Vendor or Source||Status|
|Apple Computer, Inc.||not vulnerable|
|Berkeley SW Design, Inc. (BSDI)||not vulnerable|
|Data General Corp.||not vulnerable|
|Digital Equipment Corp.||vulnerable, patches available|
|Free BSD||not vulnerable|
|NeXT, Inc.||not vulnerable|
|The Santa Cruz Operation (SCO)||see note in Appendix A|
|Solbourne (Grumman)||vulnerable - contact vendor|
|Sun Microsystems, Inc.||SunOS 4.x vulnerable, patches available,|
patch revisions coming soon
|Solaris 2.x not vulnerable|
B. Replace /bin/mail with mail.local.If you cannot obtain a vendor-supplied replacement for /bin/mail, the CERT Coordination Center recommends using mail.local as a replacement for /bin/mail.
Although the current version of mail.local is not a perfect solution, it addresses the vulnerabilities currently being exploited in /bin/mail.
mail.local is now provided with the lastest version of sendmail. That version can be found at
The original version of mail.local has been tested on SunOS 4.1 and Ultrix 4.X systems.
Mail.local.c for BSD 4.3 systems, along with a README file containing installation instructions, can be found on the anonymous FTP servers listed below.
Appendix A: Vendor InformationBelow is information we have received from vendors who have patches available or upcoming for the vulnerabilities described in this advisory, as well as vendors who have confirmed that their products are not vulnerable. If your vendor's name is not in one of these lists, contact the vendor directly for information on whether their version of sendmail is vulnerable and, if so, the status of patches to address the vulnerabilities.
NOT VULNERABLEThe following vendors have reported that their products are NOT vulnerable.
Apple Computer, Inc.
Berkeley SW Design, Inc. (BSDI)
Data General Corp.
The Santa Cruz Operation (SCO) - not vulnerable, but see note below
Sun Microsystems, Inc. - Solaris 2.x (SunOS 4.x is vulnerable; see below)
VULNERABLEWe have reports that the following vendors' products ARE vulnerable. Patch information is provided below.
Digital Equipment Corporation
|Vulnerable:||DEC OSF/1 versions 1.2, 1.3, and 2.0|
DEC ULTRIX versions 4.3, 4.3A, and 4.4
Obtain and install the appropriate patch according to the instructions included with the patch. The patch that corrects the /bin/mail problem in each case is part of a comprehensive Security Enhanced Kit that addresses other problems as well. This kit has been available since May 17, 1994. It is described in DEC security advisory #0505 and in CERT bulletin VB-94:02.
- DEC OSF/1
Upgrade/install OSF/1 to a minimum of V2.0 and install Security Enhanced Kit CSCPAT_4061 v1.0.
Upgrade/install ULTRIX to a minimum of V4.4 and install Security Enhanced Kit CSCPAT_4060 v1.0.
The Santa Cruz Operation (SCO)SCO's version of /bin/mail is not vulnerable to the problems mentioned in this advisory. SCO's /bin/mail is not setuid-root. However, SCO's /bin/mail has other security-related issues that are fixed by SCO's Support Level Supplement (SLS) uod392a. To get this:
|ftp:||ftp.sco.COM:/SLS/uod392a.Z||(compressed disk image)|
SolbourneGrumman System Support Corporation now performs all Solbourne software and hardware support. Please contact them for further information.
Sun Microsystems, Inc.Current patches are listed below:
The patches can be obtained from local Sun Answer Centers and through anonymous FTP from ftp.uu.net in the /systems/sun/sun-dist directory. In Europe, the patches are available from mcsun.eu.net in the /sun/fixes directory.
The CERT Coordination Center thanks Eric Allman, Wolfgang Ley, Karl Strickland, Wietse Venema, and Neil Woods for their contributions to mail.local.
Copyright 1995, 1996 Carnegie Mellon University.
Sep. 23 1997 Updated Copyright statement Nov. 21, 1996 Removed Appendices B & C. Sec. B, paragraph 3 - updated information about the location of mail.local. Aug. 30, 1996 Information previously in the README was inserted into the advisory, and URL formats were updated. June 09, 1995 Appendix A - corrected patch information from Sun.