----------------------------------------------------------------------------- Pine Internet Security Advisory
----------------------------------------------------------------------------- Advisory ID : PINE-CERT-20020401 Authors : Joost Pol <[EMAIL PROTECTED]> 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 ______________________ ============================================================================= FreeBSD-SA-02:23.stdio Security Advisory The FreeBSD Project Topic: insecure handling of stdio file descriptors Category: core Module: kernel Announced: 2002-04-22 Credits: Joost Pol <[EMAIL PROTECTED]> Affects: All releases of FreeBSD up to and including 4.5-RELEASE 4.5-STABLE prior to the correction date Corrected: 2002-04-21 13:06:45 UTC (RELENG_4) 2002-04-21 13:08:57 UTC (RELENG_4_5) 2002-04-21 13:10:51 UTC (RELENG_4_4) FreeBSD only: NO I. Background By convention, POSIX systems associate file descriptors 0, 1, and 2 with standard input, standard output, and standard error, respectively. Almost all applications give these stdio file descriptors special significance, such as writing error messages to standard error (file descriptor 2). In new processes, all file descriptors are duplicated from the parent process. Unless these descriptors are marked close-on-exec, they retain their state during an exec. All POSIX systems assign file descriptors in sequential order, starting with the lowest unused file descriptor. For example, if a newly exec'd process has file descriptors 0 and 1 open, but file descriptor 2 closed, and then opens a file, the new file descriptor is guaranteed to be 2 (standard error). II. Problem Description Some programs are set-user-id or set-group-id, and therefore run with increased privileges. If such a program is started with some of the stdio file descriptors closed, the program may open a file and inadvertently associate it with standard input, standard output, or standard error. The program may then read data from or write data to the file inappropriately. If the file is one that the user would normally not have privileges to open, this may result in an opportunity for privilege escalation. III. Impact Local users may gain superuser privileges. It is known that the `keyinit' set-user-id program is exploitable using this method. There may be other programs that are exploitable. IV. Workaround None. The set-user-id bit may be removed from `keyinit' using the following command, but note that there may be other programs that can be exploited. # chmod 0555 /usr/bin/keyinit V. Solution 1) Upgrade your vulnerable system to 4.5-STABLE; or to either of the RELENG_4_5 (4.5-RELEASE-p4) or RELENG_4_4 (4.4-RELEASE-p11) security branches dated after the respective correction dates. 2) To patch your present system: a) Download the relevant patch from the location below, and verify the detached PGP signature using your PGP utility. # fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-02:23/stdio.patch # fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-02:23/stdio.patch.asc b) Execute the following commands as root: # cd /usr/src # patch < /path/to/patch c) Recompile your kernel as described in http://www.freebsd.org/handbook/kernelconfig.html and reboot the system. VI. Correction details The following list contains the revision numbers of each file that was corrected in FreeBSD. Path Revision Branch - ------------------------------------------------------------------------- sys/sys/filedesc.h RELENG_4 1.19.2.4 RELENG_4_5 1.19.2.3.6.1 RELENG_4_4 1.19.2.3.4.1 sys/kern/kern_exec.c RELENG_4 1.107.2.14 RELENG_4_5 1.107.2.13.2.1 RELENG_4_4 1.107.2.8.2.2 sys/kern/kern_descrip.c RELENG_4 1.81.2.11 RELENG_4_5 1.81.2.9.2.1 RELENG_4_4 1.81.2.8.2.1 sys/conf/newvers.sh RELENG_4_5 1.44.2.20.2.5 RELENG_4_4 1.44.2.17.2.10 - ------------------------------------------------------------------------- VII. References PINE-CERT-20020401 <URL:http://www.pine.nl/advisories/pine-cert-20020401.txt> -------------------------------------- Catalin Macsim Phone: 092-756838 Network Coordonator - Nordnet Botosani Network Administrator - Petar Software __________________________________________________________ Send 'unsubscribe rofug' to [EMAIL PROTECTED] to unsubscribe
