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Home » Security Advisories» FreeBSD » Sendmail pipe vuln

Sendmail pipe vuln

Sendmail has the ability to deliver mail to a program on the local system via a pipe. This feature is often used to support automatic mail filtering and vacation programs. This provides a very flexible way to deliver information to an automated task running on a mailserver. Unfortunately, this allows unprivileged users to write tasks that may not properly check for common attacks via the program delivery system.

  • Vendor: FreeBSD
  • Vendor ID: FreeBSD-SA-96:03
  • Date: April 20, 1996


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=======================================================================
FreeBSD-SA-96:03 Security Advisory
FreeBSD, Inc.

Topic: *suggested action only* sendmail smrsh now available

Category: core
Module: sendmail
Announced: 1996-04-20
Affects: FreeBSD 2.1.0 and earlier distributions
Corrected: 1996-04-21 2.2-current and 2.1-stable sources
FreeBSD only: no

Patches: ftp://freebsd.org/pub/CERT/patches/SA-96:03/

=======================================================================

I. Background

The sendmail mail transfer agent has a rather poor reputation
for security related problems. FreeBSD ships a version of
sendmail that has all known security problems fixed, but this
doesn't mean there won't be more found in the future.

The author of sendmail recognized this posibility and has
included a new utility called "smrsh". The FreeBSD Project
would like to encourage system administrators to use this
utility as a hedge against future possible security holes.


II. Problem Description

Sendmail has the ability to deliver mail to a program on the
local system via a pipe. This feature is often used to
support automatic mail filtering and vacation programs.

This provides a very flexible way to deliver information to
an automated task running on a mailserver. Unfortunately,
this allows unprivileged users to write tasks that may not
properly check for common attacks via the program delivery
system.

The next release of FreeBSD will now install the sendmail
restricted shell utility, smrsh in /usr/libexec and create
the directory /usr/libexec/sm.bin to hold programs that
may be executed by sendmail to deliver mail to pipes.


III. Impact

There is no known security impact on FreeBSD systems at the
of this document's publication. There is no direct requirement
to install the smrsh utility.

The FreeBSD Project suggests using smrsh in conjunction with
sendmail in environments where the local system administrator
believes there is a need to protect against as-of-yet undiscovered
security holes in sendmail.

Use of this utility is /not/ enabled by default in standard
sendmail configuration files distributed by FreeBSD to retain
backwards compatibility with previous sendmail operation. Use
of this utility may break functionality that users expect.
Please read the smrsh(8) manual page and/or the README file in
/usr/src/usr.sbin/sendmail/smrsh BEFORE attempting to use smrsh.


IV. Solution(s)

This program is available in the 2.1-stable and 2.2-current
source code distributions. It is not compiled, installed,
or enabled in FreeBSD 2.1.0 by default.

The Apache Group released version 1.05 of the daemon which fixes
this vulnerability. The FreeBSD Project updated the ports and
packages system to use this new daemon.

Interested parties may obtain an updated pre-compiled FreeBSD
package from:

ftp://ftp.freebsd.org/pub/FreeBSD/packages-current/www/apache-1.0.5.tgz

and an updated "automatic port" from the directory hierarchy:

ftp://ftp.freebsd.org/pub/FreeBSD/ports-current/www/apache.tar.gz


=======================================================================
FreeBSD, Inc.

Web Site: http://www.freebsd.org/
Confidential contacts: [email protected]
PGP Key: ftp://freebsd.org/pub/CERT/public_key.asc
Security notifications: [email protected]
Security public discussion: [email protected]

Notice: Any patches in this document may not apply cleanly due to
modifications caused by digital signature or mailer software.
Please reference the URL listed at the top of this document
for original copies of all patches if necessary.
=======================================================================

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