FreeBSD Security Advisories
2000-Nov-20 13:39 UTC
FreeBSD Security Advisory: FreeBSD-SA-00:68.ncurses [REVISED]
-----BEGIN PGP SIGNED MESSAGE----- ============================================================================FreeBSD-SA-00:68 Security Advisory FreeBSD, Inc. Topic: ncurses allows local privilege escalation [REVISED] Category: core, ports Module: ncurses Announced: 2000-11-13 Revised: 2000-11-20 Affects: FreeBSD 5.0-CURRENT, 4.x prior to the correction date. FreeBSD 3.x not yet fixed. Corrected: 2000-10-11 (FreeBSD 4.1.1-STABLE) 2000-11-10 (ncurses port) Credits: Jouko Pynnonen <jouko@SOLUTIONS.FI> FreeBSD only: NO 0. Revision History v1.0 2000-11-13 Initial release v1.1 2000-11-20 Corrected status of 3.x, referenced ncurses port I. Background ncurses is a text-mode display library used for formatting the output of applications on a variety of terminals. It is externally maintained, contributed code which is included in FreeBSD by default. II. Problem Description There exists an overflowable buffer in the libncurses library in the processing of cursor movement capabilities. An attacker can force a privileged application to use the attacker's termcap file containing a specially crafted terminal entry, which will trigger the vulnerability when the vulnerable ncurses code is called. This allows them to execute arbitrary code on the local system with the privileges of the exploited binary. The systat utility included in the FreeBSD base system is known to use vulnerable ncurses routines. It 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. There may be other vulnerable applications included in the FreeBSD base system, but no others are confirmed to be vulnerable due to the difficulty in identifying a complete list of vulnerable ncurses functions. However the following is a complete list of FreeBSD system binaries which link against ncurses and run with increased privileges. They may or may not be vulnerable to exploitation. /usr/sbin/lpc /usr/bin/top /usr/bin/systat FreeBSD 3.x and earlier versions use a very old, customized version of ncurses which is difficult to update without breaking backwards-compatibility. The update was made for FreeBSD 4.0, but 3.x will not be updated to the newer version. At this stage the vulnerability has not been fixed in FreeBSD 3.x. The ncurses port (versions prior to 5.2) also contains this vulnerability. It was corrected prior to the release of FreeBSD 4.2. III. Impact Certain setuid/setgid software (including FreeBSD base system utilities and third party ports/packages) may be vulnerable to a local exploit yielding privileged access. The /usr/bin/systat utility is known to be vulnerable to this problem in ncurses. At this time is unknown whether /usr/bin/top and /usr/sbin/lpc are also affected. The problems were corrected prior to the release of FreeBSD 4.2. IV. Workaround It is not feasible to reliably detect binaries which are vulnerable to the ncurses vulnerability, however the provided utility will scan for privileged binaries which use ncurses and which may potentially be vulnerable. Some of the binaries reported may not in fact be vulnerable, but should be recompiled anyway for maximum assurance of security. Statically linked binaries which are identified as potentially vulnerable should be recompiled from source code if possible, after patching and recompiling libc, in order to correct the vulnerability. Dynamically linked binaries will be corrected by simply patching and recompiling libc as described below. As an interim measure, consider removing any identified setuid or setgid binary, removing set[ug]id privileges from the file, or limiting the file access permissions, as appropriate. Of course, it is possible that some of the identified files may be required for the correct operation of your local system, in which case there is no clear workaround except for limiting the set of users who may run the binaries, by an appropriate use of user groups and removing the "o+x" file permission bit. 1) Download the 'scan_ncurses.sh' and 'test_ncurses.sh' scripts from ftp://ftp.freebsd.org/pub/FreeBSD/CERT/tools/SA-00:68/scan_ncurses.sh ftp://ftp.freebsd.org/pub/FreeBSD/CERT/tools/SA-00:68/test_ncurses.sh e.g. with the fetch(1) command: # fetch ftp://ftp.freebsd.org/pub/FreeBSD/CERT/tools/SA-00:68/scan_ncurses.sh Receiving scan_ncurses.sh (381 bytes): 100% 381 bytes transferred in 0.1 seconds (7.03 kBps) # fetch ftp://ftp.freebsd.org/pub/FreeBSD/CERT/tools/SA-00:68/test_ncurses.sh Receiving test_ncurses.sh (604 bytes): 100% 604 bytes transferred in 0.1 seconds (6.55 kBps) 2) Verify the md5 checksums and compare to the value below: # md5 scan_ncurses.sh MD5 (scan_ncurses.sh) = 597f63af701253f053581aa1821cbac1 # md5 test_ncurses.sh MD5 (test_ncurses.sh) = 12491ceb15415df7682e3797de53223e 3) Run the scan_ncurses.sh script against your system: # chmod a+x ./test_ncurses.sh # sh scan_ncurses.sh ./test_ncurses.sh / This will scan your entire system for setuid or setgid binaries which make use of the ncurses library. Each returned binary should be examined (e.g. with 'ls -l' and/or other tools) to determine what security risk it poses to your local environment, e.g. whether it can be run by arbitrary local users who may be able to exploit it to gain privileges. 4) Remove the binaries, or reduce their file permissions, as appropriate. V. Solution Upgrade your vulnerable FreeBSD system to 4.1.1-STABLE after the correction date, or patch your present system source code and rebuild. Then run the scan_ncurses.sh script as instructed in section IV and identify any statically-linked binaries as reported by the script. These should either be removed, recompiled, or have privileges restricted to secure them against this vulnerability (since statically-linked binaries will not be affected by simply recompiling the shared libc library). To patch your present system: download the updated ncurses code from the below location, and execute the following commands as root: # fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-00:68/ncurses.tar.gz # fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-00:68/ncurses.tar.gz.asc Verify the detached PGP signature using your PGP utility. cd /usr/src tar xvfz /path/to/ncurses.tar.gz cd /usr/src/lib/libncurses make all make install In contrast to the usual practise, a simple patch fixing the security vulnerability is not provided because the vendor did not make one available, and the updated ncurses snapshot which fixed it contains numerous other changes whose purpose and relation to the fix was unclear. [ncurses port] If you have installed a vulnerable version of the ncurses port, one of the following steps may be used to upgrade it: 1) Upgrade your entire ports collection and rebuild the ncurses port. 2) Deinstall the old package and install a new package dated after the correction date, obtained from: ftp://ftp.FreeBSD.org/pub/FreeBSD/ports/i386/packages-3-stable/devel/ncurses-5.2.tgz ftp://ftp.FreeBSD.org/pub/FreeBSD/ports/i386/packages-4-stable/devel/ncurses-5.2.tgz ftp://ftp.FreeBSD.org/pub/FreeBSD/ports/alpha/packages-4-stable/devel/ncurses-5.2.tgz ftp://ftp.FreeBSD.org/pub/FreeBSD/ports/i386/packages-5-current/devel/ncurses-5.2.tgz ftp://ftp.FreeBSD.org/pub/FreeBSD/ports/alpha/packages-5-current/devel/ncurses-5.2.tgz 3) download a new port skeleton for the ncurses port from: http://www.freebsd.org/ports/ and use it to rebuild the port. 4) Use the portcheckout utility to automate option (3) above. The portcheckout port is available in /usr/ports/devel/portcheckout or the package can be obtained from: ftp://ftp.FreeBSD.org/pub/FreeBSD/ports/i386/packages-3-stable/devel/portcheckout-2.0.tgz ftp://ftp.FreeBSD.org/pub/FreeBSD/ports/i386/packages-4-stable/devel/portcheckout-2.0.tgz ftp://ftp.FreeBSD.org/pub/FreeBSD/ports/alpha/packages-4-stable/devel/portcheckout-2.0.tgz ftp://ftp.FreeBSD.org/pub/FreeBSD/ports/i386/packages-5-current/devel/portcheckout-2.0.tgz ftp://ftp.FreeBSD.org/pub/FreeBSD/ports/alpha/packages-5-current/devel/portcheckout-2.0.tgz -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.0.4 (FreeBSD) Comment: For info see http://www.gnupg.org iQCVAwUBOhmaFlUuHi5z0oilAQG5MwP9FStZoFKPCqfciIbIcFrE0wLYuEOeI24S j9D4rSwU1ALzHB7DMpeXmju5pDRROmgUTIOGnBN9FcXZly4lDN3Y9yyIeW6Ia5UZ wWbkhxsn573kD3P00WHAB1F1ccbbK4+SPNLkdJDgyyqAC4SdgeJEg5+z+Wcx7d3E t/Xsv/X1ylA=ZiMW -----END PGP SIGNATURE----- This is the moderated mailing list freebsd-announce. 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