Exploit Exercises - Protostar Net 0

2 minute read Feb 8, 2012 Comments
I recently started looking at the “Net” problems in Protostar, and found them to be quite a fun change in pace. Starting with Net 0, we are given the following code: #include "../common/common.c" #define NAME "net0" #define UID 999 #define GID 999 #define PORT 2999 void run() { unsigned int i; unsigned int wanted; wanted = random(); printf("Please send '%d' as a little endian 32bit int\n", wanted); if(fread(&i, sizeof(i), 1, stdin) == NULL) { errx(1, ":(\n"); } if(i == wanted) { printf("Thank you sir/madam\n"); } else { printf("I'm sorry, you sent %d instead\n", i); } } int main(int argc, char **argv, char **envp) { int fd; char *username; /* Run the process as a daemon */ background_process(NAME, UID, GID); /* Wait for socket activity and return */ fd = serve_forever(PORT); /* Set the client socket to STDIN, STDOUT, and STDERR */ set_io(fd); /* Don't do this :> */ srandom(time(NULL)); run(); } I started to analyze this program, to figure out what I was even supposed to do.
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Exploit Exercises - Protostar Final 1

11 minute read Feb 5, 2012 Comments
Since I’ve been doing a lot of the format string exploits lately, I decided to do the Final 1 challenge. We start out the challenge by being given the following code: #include "../common/common.c" #include <syslog.h> #define NAME "final1" #define UID 0 #define GID 0 #define PORT 2994 char username[128]; char hostname[64]; void logit(char *pw) { char buf[512]; snprintf(buf, sizeof(buf), "Login from %s as [%s] with password [%s]\n", hostname, username, pw); syslog(LOG_USER|LOG_DEBUG, buf); } void trim(char *str) { char *q; q = strchr(str, '\r'); if(q) *q = 0; q = strchr(str, '\n'); if(q) *q = 0; } void parser() { char line[128]; printf("[final1] $ "); while(fgets(line, sizeof(line)-1, stdin)) { trim(line); if(strncmp(line, "username ", 9) == 0) { strcpy(username, line+9); } else if(strncmp(line, "login ", 6) == 0) { if(username[0] == 0) { printf("invalid protocol\n"); } else { logit(line + 6); printf("login failed\n"); } } printf("[final1] $ "); } } void getipport() { int l; struct sockaddr_in sin; l = sizeof(struct sockaddr_in); if(getpeername(0, &sin, &l) == -1) { err(1, "you don't exist"); } sprintf(hostname, "%s:%d", inet_ntoa(sin.
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Exploit Exercises - Protostar Format 4

5 minute read Feb 2, 2012 Comments
Next up is the last challenge in the Format String series, Format 4. It starts out with the following code: #include <stdlib.h> #include <unistd.h> #include <stdio.h> #include <string.h> int target; void hello() { printf("code execution redirected! you win\n"); _exit(1); } void vuln() { char buffer[512]; fgets(buffer, sizeof(buffer), stdin); printf(buffer); exit(1); } int main(int argc, char **argv) { vuln(); } What initially caught my eye was the fact that there was a call to “exit()” as well as “_exit()”.
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Exploit Exercises - Protostar Format 3

5 minute read Feb 1, 2012 Comments
Continuing in the String Format section, the next challenge we run across is Format 3. We’re first given the following code: #include <stdlib.h> #include <unistd.h> #include <stdio.h> #include <string.h> int target; void printbuffer(char *string) { printf(string); } void vuln() { char buffer[512]; fgets(buffer, sizeof(buffer), stdin); printbuffer(buffer); if(target == 0x01025544) { printf("you have modified the target :)\n"); } else { printf("target is %08x :(\n", target); } } int main(int argc, char **argv) { vuln(); } This seems to be just like Format 2, except that we have to modify all 8 bytes instead of just 2.
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Exploit Exercises - Protostar Format 2

2 minute read Jan 31, 2012 Comments
Continuing from where we left off, we arrive at Format 2. It presents us with the following code: #include <stdlib.h> #include <unistd.h> #include <stdio.h> #include <string.h> int target; void vuln() { char buffer[512]; fgets(buffer, sizeof(buffer), stdin); printf(buffer); if(target == 64) { printf("you have modified the target :)\n"); } else { printf("target is %d :(\n", target); } } int main(int argc, char **argv) { vuln(); } This challenge seems very similar to Format 1, in all but 2 ways:
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Exploit Exercises - Protostar Format 1

3 minute read Jan 30, 2012 Comments
Following the Format 0 challenge, I’ve had to do a bunch of reading on how format string exploits work on a very low level. Some resources that I’ve found greatly useful: Hacking: The Art of Exploitation, 2nd Edition Exploiting Format String Vulnerabilities SecurityTube.net Format String Vulnerabilities Megaprimer With this challenge, we’re given some c code in which we are to find the vulnerability. #include <stdlib.h> #include <unistd.h> #include <stdio.h> #include <string.
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Exploit Exercises - Protostar Format 0

3 minute read Jan 24, 2012 Comments
I’ll be honest, I’m new to format string exploits. I’ve been more experienced with stack overflows, and a little with heap overflows. So hopefully this information is correct, as it’s from my current understanding. Protostar Format 0 starts us off with the following vulnerable code: #include <stdlib.h> #include <unistd.h> #include <stdio.h> #include <string.h> void vuln(char *string) { volatile int target; char buffer[64]; target = 0; sprintf(buffer, string); if(target == 0xdeadbeef) { printf("you have hit the target correctly :)\n"); } } int main(int argc, char **argv) { vuln(argv[1]); } Looking at this code, somehow we have to get the variable, “target”, which is never set anywhere other than to “0”, to equal “0xdeadbeef”.
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Exploit Exercises - Protostar Final 0

6 minute read Jan 22, 2012 Comments
I for some reason decided to look at the set of “final” challenges, and found the first one to be not too difficult. We start with the following code being given to us: #include "../common/common.c" #define NAME "final0" #define UID 0 #define GID 0 #define PORT 2995 /* * Read the username in from the network */ char *get_username() { char buffer[512]; char *q; int i; memset(buffer, 0, sizeof(buffer)); gets(buffer); /* Strip off trailing new line characters */ q = strchr(buffer, '\n'); if(q) *q = 0; q = strchr(buffer, '\r'); if(q) *q = 0; /* Convert to lower case */ for(i = 0; i &lt; strlen(buffer); i++) { buffer[i] = toupper(buffer[i]); } /* Duplicate the string and return it */ return strdup(buffer); } int main(int argc, char **argv, char **envp) { int fd; char *username; /* Run the process as a daemon */ background_process(NAME, UID, GID); /* Wait for socket activity and return */ fd = serve_forever(PORT); /* Set the client socket to STDIN, STDOUT, and STDERR */ set_io(fd); username = get_username(); printf("No such user %s\n", username); } This is a somewhat standard buffer overflow.
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Exploit Exercises - Protostar Heap 1

5 minute read Jan 12, 2012 Comments
This challenge was different for me. The previous heap challenge was easy to pretend it was just a simple stack overflow. This one worked very different, and brought some different challenges with it. You first start out with the following code: #include <stdlib.h> #include <unistd.h> #include <string.h> #include <stdio.h> #include <sys/types.h> struct internet { int priority; char *name; }; void winner() { printf("and we have a winner @ %d\n", time(NULL)); } int main(int argc, char **argv) { struct internet *i1, *i2, *i3; i1 = malloc(sizeof(struct internet)); i1->priority = 1; i1->name = malloc(8); i2 = malloc(sizeof(struct internet)); i2->priority = 2; i2->name = malloc(8); strcpy(i1->name, argv[1]); strcpy(i2->name, argv[2]); printf("and that's a wrap folks!
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Exploit Exercises - Protostar Heap 0

2 minute read Jan 10, 2012 Comments
Now that I’ve completed all of the Stack section of protostar, I’ve started to move onto Heap. The first of these challenges, is Heap 0. We are given the following code: #include <stdlib.h> #include <unistd.h> #include <string.h> #include <stdio.h> #include <sys/types.h> struct data { char name[64]; }; struct fp { int (*fp)(); }; void winner() { printf("level passed\n"); } void nowinner() { printf("level has not been passed\n"); } int main(int argc, char **argv) { struct data *d; struct fp *f; d = malloc(sizeof(struct data)); f = malloc(sizeof(struct fp)); f->fp = nowinner; printf("data is at %p, fp is at %p\n", d, f); strcpy(d->name, argv[1]); f->fp(); } I first needed to find the offset to where I could overwrite the EIP, so I connected to my other machine with the Metasploit Framework installed, and generated a unique string.
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