[ SOURCE: http://www.secureroot.com/security/advisories/9737038570.html ] -----BEGIN PGP SIGNED MESSAGE----- ============================================================================= FreeBSD-SA-00:62 Security Advisory FreeBSD, Inc. Topic: top allows reading of kernel memory [REISSUED] Category: core Module: top Announced: 2000-11-01 Reissued: 2000-11-06 Credits: vort@wiretapped.net via OpenBSD Affects: FreeBSD 3.x (all releases), FreeBSD 4.x (all releases prior to 4.2), FreeBSD 3.5.1-STABLE and 4.1.1-STABLE prior to the correction date. Corrected: 2000-11-04 (FreeBSD 4.1.1-STABLE) 2000-11-05 (FreeBSD 3.5.1-STABLE) FreeBSD only: NO 0. Revision History v1.0 2000-11-01 Initial release v1.1 2000-11-06 Updated patch released. I. Background top is a utility for displaying current system resource statistics such as process CPU and memory use. It is externally-maintained, contributed software which is included in FreeBSD by default. II. Problem Description A "format string vulnerability" was discovered in the top(1) utility which allows unprivileged local users to cause the top process to execute arbitrary code. The top utility runs with increased privileges as a member of the kmem group, which allows it to read from kernel memory (but not write to it). A process with the ability to read from kernel memory can monitor privileged data such as network traffic, disk buffers and terminal activity, and may be able to leverage this to obtain further privileges on the local system or on other systems, including root privileges. All released versions of FreeBSD prior to the correction date including 4.0, 4.1, 4.1.1 and 3.5.1 are vulnerable to this problem, but it was fixed in the 4.1.1-STABLE branch prior to the release of FreeBSD 4.2-RELEASE. III. Impact Local users can read privileged data from kernel memory which may provide information allowing them to further increase their local or remote system access privileges. IV. Workaround Remove the setgid bit on the top utilities. This has the side-effect that users who are not a member of the kmem group or who are not the superuser cannot use the top utility. # chmod g-s /usr/bin/top V. Solution One of the following: 1) Upgrade your vulnerable FreeBSD system to 4.1.1-STABLE or 3.5.1-STABLE after the respective correction dates. 2) Apply the patch below and recompile the relevant files: NOTE: The original version of this advisory contained an incomplete patch which does not fully eliminate the security vulnerability. The additional vulnerability was pointed out by Przemyslaw Frasunek . Either save this advisory to a file, or download the patch and detached PGP signature from the following locations, and verify the signature using your PGP utility. ftp://ftp.freebsd.org/pub/FreeBSD/CERT/patches/SA-00:62/top.patch.v1.1 ftp://ftp.freebsd.org/pub/FreeBSD/CERT/patches/SA-00:62/top.patch.v1.1.asc Execute the following commands as root: # cd /usr/src/contrib/top # patch -p < /path/to/patch_or_advisory # cd /usr/src/usr.bin/top # make depend && make all install Patch for vulnerable systems: Index: display.c =================================================================== RCS file: /mnt/ncvs/src/contrib/top/display.c,v retrieving revision 1.4 retrieving revision 1.5 diff -u -r1.4 -r1.5 --- display.c 1999/01/09 20:20:33 1.4 +++ display.c 2000/10/04 23:34:16 1.5 @@ -829,7 +831,7 @@ register int i; /* first, format the message */ - (void) sprintf(next_msg, msgfmt, a1, a2, a3); + (void) snprintf(next_msg, sizeof(next_msg), msgfmt, a1, a2, a3); if (msglen > 0) { Index: top.c =================================================================== RCS file: /mnt/ncvs/src/contrib/top/top.c,v retrieving revision 1.4 retrieving revision 1.5 diff -u -r1.4 -r1.5 --- top.c 1999/01/09 20:20:34 1.4 +++ top.c 2000/10/04 23:34:16 1.5 @@ -807,7 +809,7 @@ { if ((errmsg = kill_procs(tempbuf2)) != NULL) { - new_message(MT_standout, errmsg); + new_message(MT_standout, "%s", errmsg); putchar('\r'); no_command = Yes; } Index: top.c =================================================================== RCS file: /mnt/ncvs/src/contrib/top/top.c,v retrieving revision 1.5 retrieving revision 1.6 diff -u -r1.5 -r1.6 --- top.c 2000/10/04 23:34:16 1.5 +++ top.c 2000/11/03 22:00:10 1.6 @@ -826,7 +826,7 @@ { if ((errmsg = renice_procs(tempbuf2)) != NULL) { - new_message(MT_standout, errmsg); + new_message(MT_standout, "%s", errmsg); putchar('\r'); no_command = Yes; } -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.0.4 (FreeBSD) Comment: For info see http://www.gnupg.org iQCVAwUBOgcN7lUuHi5z0oilAQFqJgP/bn4SN6FaNvazYMaVzypsEgWzofK/kdlu iWXcdZVkoFZlF4J7e6M/wRn0xS1lvNPlv5yNF4bYa7lnZHeNzS/58v94+Sze2ooV bgML9JzhfaM0Ps+/mAXO4FzGi+WryTkdZGl9KVkwT+QwuRer/bz4GoJvnrsGuBpf dXoovvpgwiA= =hVPb -----END PGP SIGNATURE-----