-----BEGIN PGP SIGNED MESSAGE----- ============================================================================= FreeBSD-SA-02:08 Security Advisory FreeBSD, Inc. Topic: race condition during exec may allow local root compromise Category: core Module: kernel Announced: 2002-01-24 Credits: Logan Gabriel , Robert Watson , Dag-Erling Smørgrav Affects: All released versions of FreeBSD 4.x prior to 4.5-RELEASE. FreeBSD 4.4-STABLE prior to the correction date. Corrected: 2002-01-22 17:22:59 UTC (4-STABLE, RELENG_4) 2002-01-23 23:05:00 UTC (4.4-RELEASE-p4, RELENG_4_4) 2002-01-23 23:05:53 UTC (4.3-RELEASE-p24, RELENG_4_3) FreeBSD only: NO I. Background When a process is started from a set-user-ID or set-group-ID binary, it is marked so that attempts to attach to it with debugging hooks fail. To allow such attachments would allow a user to subvert the process and gain elevated privileges. II. Problem Description A race condition exists in the FreeBSD exec system call implementation. It is possible for a user to attach a debugger to a process while it is exec'ing, but before the kernel has determined that the process is set-user-ID or set-group-ID. All versions of FreeBSD 4.x prior to FreeBSD 4.5-RELEASE are vulnerable to this problem. The problem has been corrected by marking processes that have started but not yet completed exec with an `in-exec' state. Attempts to debug a process in the in-exec state will fail. III. Impact Local users may be able to gain increased privileges on the local system. IV. Workaround None. Do not allow untrusted users to gain access to the local system. V. Solution One of the following: 1) Upgrade your vulnerable FreeBSD system to 4.4-STABLE, or the RELENG_4_3 or RELENG_4_4 security branch, dated after the respective correction date. 2) To patch your present system: a) Download the relevant patch from the following location: [FreeBSD 4.4-STABLE, or RELENG_4_3 and RELENG_4_4 security branches] ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-02:08/exec.patch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-02:08/exec.patch.asc [FreeBSD 4.3-RELEASE only] ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-02:08/exec-43R.patch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-02:08/exec-43R.patch.asc b) Verify the detached PGP signature using your PGP utility. c) Execute the following commands as root: # cd /usr/src # patch -p < /path/to/patch Recompile your kernel as described in http://www.freebsd.org/handbook/kernelconfig.html and reboot the system. 3) FreeBSD 4.4-RELEASE systems: An experimental upgrade package is available for users who wish to provide testing and feedback on the binary upgrade process. This package may be installed on FreeBSD 4.4-RELEASE systems only, and is intended for use on systems for which source patching is not practical or convenient. If you use the upgrade package, feedback (positive or negative) to security-officer@FreeBSD.org is requested so we can improve the process for future advisories. Since this vulnerability involves the FreeBSD kernel which is often locally customized on installed systems, a universal binary upgrade package is not feasible. This package includes a patched version of the GENERIC kernel which should be suitable for use on many systems. Systems requiring a customized kernel must use an alternative solution. During the installation procedure, backup copies are made of the files which are replaced by the package. These backup copies will be reinstalled if the package is removed, reverting the system to a pre-patched state. # fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/packages/SA-02:08/security-patch-exec-02.08.tgz # fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/packages/SA-02:08/security-patch-exec-02.08.tgz.asc Verify the detached PGP signature using your PGP utility. # pkg_add security-patch-exec-02.08.tgz The new kernel is named /kernel.GENERIC to avoid conflict with the default kernel name (``/kernel''). To cause the system to boot automatically with the new kernel, add the following line to /boot/loader.conf: kernel="/kernel.GENERIC" and reboot the system to load the new kernel. The old kernel is still available and can be manually loaded in the boot loader in case of problems. VI. Correction details The following list contains the $FreeBSD$ revision number of the files that were corrected in the FreeBSD source. Path Revision Branch - ------------------------------------------------------------------------- src/sys/conf/newvers.sh RELENG_4_4 1.44.2.17.2.5 RELENG_4_3 1.44.2.14.2.14 src/sys/kern/kern_exec.c RELENG_4 1.107.2.13 RELENG_4_4 1.107.2.8.2.1 RELENG_4_3 1.107.2.5.2.2 src/sys/kern/sys_process.c RELENG_4 1.51.2.3 RELENG_4_4 1.51.2.1.4.1 RELENG_4_3 1.51.2.1.2.1 src/sys/miscfs/procfs/procfs.h RELENG_4 1.32.2.3 RELENG_4_4 1.32.2.2.2.1 RELENG_4_3 1.32.2.1.2.2 src/sys/miscfs/procfs/procfs_ctl.c RELENG_4 1.20.2.2 RELENG_4_4 1.20.2.1.4.1 RELENG_4_3 1.20.2.1.2.1 src/sys/miscfs/procfs/procfs_dbregs.c RELENG_4 1.4.2.3 RELENG_4_4 1.4.2.2.2.1 RELENG_4_3 1.4.2.1.2.1 src/sys/miscfs/procfs/procfs_fpregs.c RELENG_4 1.11.2.3 RELENG_4_4 1.11.2.2.2.1 RELENG_4_3 1.11.2.1.2.1 src/sys/miscfs/procfs/procfs_mem.c RELENG_4 1.46.2.3 RELENG_4_4 1.46.2.2.2.1 RELENG_4_3 1.46.2.1.2.2 src/sys/miscfs/procfs/procfs_regs.c RELENG_4 1.10.2.3 RELENG_4_4 1.10.2.2.2.1 RELENG_4_3 1.10.2.1.2.1 src/sys/miscfs/procfs/procfs_status.c RELENG_4 1.20.2.4 RELENG_4_4 1.20.2.3.4.1 RELENG_4_3 1.20.2.3.2.1 src/sys/miscfs/procfs/procfs_vnops.c RELENG_4 1.76.2.7 RELENG_4_4 1.76.2.5.2.1 RELENG_4_3 1.76.2.3.2.2 src/sys/sys/proc.h RELENG_4 1.99.2.6 RELENG_4_4 1.99.2.5.4.1 RELENG_4_3 1.99.2.5.2.1 - ------------------------------------------------------------------------- VII. References -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.0.6 (FreeBSD) Comment: For info see http://www.gnupg.org iQCVAwUBPFCAl1UuHi5z0oilAQGyiQP/V2byHL40v23S1q4PanobNUPhKUQBKsVI OCmBowy2r7Ka0GPDFxAko/xeXnZmM9lvZ0PqMdpy5god27txxAtXmvmJjMPc3dRK SbJGvfrGSrRMvXR8rrpIOugq0mkMePiXsS8RDAkcAHAXpFF0MVuQfoaQYykn+LiV i6D4RvGxGZw= =ywM6 -----END PGP SIGNATURE-----