Sorry!! (was: Re: [cobalt-security] Is this a known bug?)

["Florian Effenberger" <florian.effenberger@xxxxxxxxxxxxx>]

Hi,

ah, man, I am such an idiot! :) It is already mentioned in this list,
sorry!

----- Original Message -----
From: "Florian Effenberger" <florian.effenberger@xxxxxxxxxxxxx>
To: <cobalt-security@xxxxxxxxxxxxxxx>
Sent: Sunday, July 23, 2000 10:30 PM
Subject: [cobalt-security] Is this a known bug?


-----BEGIN PGP SIGNED MESSAGE-----

  SENDMAIL SECURITY TEAM ADVISORY

 Sendmail Workaround for Linux Capabilities Bug

The Sendmail Consortium and Sendmail, Inc. has been informed of a
serious problem in the Linux kernel that can be used to get root
access.  This is not a sendmail security problem, although sendmail
is one of the vectors for this attack.

PROBLEM

 There is a bug in the Linux kernel capability model for versions
 through 2.2.15 that allows local users to get root.  Sendmail is
 one of the programs that can be attacked this way.  This problem
 may occur in other capabilities-based kernels.

SOLUTION

 The correct fix is to update your Linux kernel to version
 2.2.16.  This is the only way to ensure that other programs
 running on Linux cannot be attacked by this bug.

WORKAROUND

 Sendmail 8.10.2 has added a check to see if the kernel has
 this bug, and if so will refuse to run.  This version also
 does more detailed checks on certain system calls, notably
 setuid(2), to detect other possible attacks.  Although there
 are no known attacks, this version is strongly recommended,
 whether or not you have a vulnerable kernel.

 Sendmail 8.10.2 can be obtained from:

 ftp://ftp.sendmail.org/pub/sendmail/sendmail.8.10.2.tar.gz
 ftp://ftp.sendmail.org/pub/sendmail/sendmail.8.10.2.tar.Z
 ftp://ftp.sendmail.org/pub/sendmail/sendmail.8.10.2.tar.sig

        and has MD5 signatures:

 acb8b6f50869a058a9baaa4fb4692c4b sendmail.8.10.2.tar.Z
 00705e5ca3412604cebd052e0d7aefcd sendmail.8.10.2.tar.gz
 92dca37fb68a2a44f02c292656c123b6 sendmail.8.10.2.tar.sig

 You only need one of the first two files (either the gzip'ed
 version or the compressed version).  The .sig file is a PGP
 signatures of the tar file (after uncompressing it).  It is
 signed with the Sendmail Signing Key/2000, available on the web
 site (http://www.sendmail.org/) or on the public key servers.

 Note however that installing this sendmail patch does not
 fully protect you from attack.  Other programs are probably
 vulnerable.

ACKNOWLEDGEMENTS

 Several people contributed to this advisory.  Wojciech Purczynski
 of Elzab Soft first identified the problem.  Alan Cox verified
 and patched the Linux kernel bug.  Gregory Neil Shapiro and other
 members of the Sendmail Consortium helped identify the problem
 and produce the sendmail workaround.

DETAILS OF THE VULNERABILITY

 The problem lies in the setcap(2) call, which is not documented
 on most Linux-based systems (we think there might be a man page
 on Mandrake).  This call, based on the unratified Posix 1e draft,
 attempts to break down root permissions into a series of
 capabilities.  Normally root has all capabilities and normal
 users have none of the capabilities.

 One such capability is the ability of a process to do an
 arbitrary setuid(2) call.  As documented in ISO/IEC 9945-1
 (ANSI/IEEE Std 1003.1) POSIX Part 1:

  4.2.2.2 Description
  ...
     If {_POSIX_SAVED_IDS} is defined:

     (1) If the process has appropriate privileges, the
         setuid() function sets the real user ID, effective
         user ID, and the saved set-user-ID to uid.

     (2) If the process does not have the appropriate
         privileges, but uid is equal to the real user ID
         or the saved set-user-ID, the setuid() function
         sets the effective user ID to uid; the real user
         ID and saved set-user-ID remain unchanged by this
         function call.

 The CAP_SETUID capability represents the "appropriate privileges".

 Normally this would not be an issue, since a setuid root program
 would simply have capability reinstated.  However, Linux has
 an added capability CAP_SETPCAP that controls the ability of a
 process to inherit capabilities; this capability does affect
 setuid programs.  It is possible to set the capabilities such
 that a setuid program does not have "appropriate privileges."
 The effect of this is that a root program cannot fully give up
 its root privileges (since the saved set-user-ID cannot be
 reset).

 Note that checking the return value from setuid() is insufficient;
 the setuid(getuid()) succeeds even when the process does not have
 "appropriate privileges."

 The sendmail patch attempts a setuid(0) after a setuid(getuid());
 under normal circumstances this should fail (unless of course
 the real uid is root).  If this setuid(0) succeeds, then the
 kernel has failed to properly give up permissions and sendmail
 will refuse to continue running.

 This problem can, of course, appear in any setuid root program
 that attempts to cede special permissions.

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