cscg24-guacamole

CSCG 2024 Challenge 'Guacamole Mashup'
git clone https://git.sinitax.com/sinitax/cscg24-guacamole
Log | Files | Refs | sfeed.txt

flagtool.c (1272B)

      1#include <stdio.h>
      2#include <string.h>
      3#include <stdlib.h>
      4#include <unistd.h>
      5
      6int main(int argc, char** argv) {
      7    if (argc <= 1) {
      8        printf("Usage: <flagtool> <writeflag/readflag>\nWrites flag to /root/\nUsed as SUID binary for CTF challenges\n");
      9        return -1;
     10    }
     11
     12    setuid(0);
     13    setgid(0);
     14    seteuid(0);
     15
     16	if(strcmp(argv[1], "writeflag") == 0) {
     17        char* FLAG_ENV = getenv("FLAG");
     18        if (FLAG_ENV == NULL) {
     19            printf("FLAG env not set\n");
     20            return -1;
     21        }
     22
     23        FILE *f = fopen("/root/flag", "w");
     24        if (f == NULL)
     25        {
     26            printf("Error opening file!\n");
     27            exit(1);
     28        }
     29
     30        /* print some text */
     31        fprintf(f, "%s\n", FLAG_ENV);
     32        fclose(f);
     33    }
     34
     35    else if(strcmp(argv[1], "readflag") == 0) {
     36        char content[256];
     37        FILE *f = fopen("/root/flag", "r");
     38        if (f == NULL)
     39        {
     40            printf("Error opening file!\n");
     41            exit(1);
     42        }
     43
     44        fgets(content, sizeof(content), f);
     45
     46        /* print some text */
     47        printf("%s\n", content);
     48        fclose(f);
     49    }
     50    else {
     51        printf("Usage: <flagtool> <writeflag/readflag>\nWrites flag to /root/\nUsed as SUID binary for CTF challenges\n");
     52    }
     53}