pwn/two-sum

pwn/two-sum/flag.c

@@ -0,0 +1,51 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+static int addIntOvf(int result, int a, int b) {
+    result = a + b;
+    if(a > 0 && b > 0 && result < 0)
+        return -1;
+    if(a < 0 && b < 0 && result > 0)
+        return -1;
+    return 0;
+}
+
+int main() {
+    int num1, num2, sum;
+    FILE *flag;
+    char c;
+
+    printf("n1 > n1 + n2 OR n2 > n1 + n2 \n");
+    fflush(stdout);
+    printf("What two positive numbers can make this possible: \n");
+    fflush(stdout);
+    
+    if (scanf("%d", &num1) && scanf("%d", &num2)) {
+        printf("You entered %d and %d\n", num1, num2);
+        fflush(stdout);
+        sum = num1 + num2;
+        if (addIntOvf(sum, num1, num2) == 0) {
+            printf("No overflow\n");
+            fflush(stdout);
+            exit(0);
+        } else if (addIntOvf(sum, num1, num2) == -1) {
+            printf("You have an integer overflow\n");
+            fflush(stdout);
+        }
+
+        if (num1 > 0 || num2 > 0) {
+            flag = fopen("flag.txt","r");
+            if(flag == NULL){
+                printf("flag not found: please run this on the server\n");
+                fflush(stdout);
+                exit(0);
+            }
+            char buf[60];
+            fgets(buf, 59, flag);
+            printf("YOUR FLAG IS: %s\n", buf);
+            fflush(stdout);
+            exit(0);
+        }
+    }
+    return 0;
+}

pwn/two-sum/output.txt

@@ -0,0 +1,8 @@
+$ nc saturn.picoctf.net 54163
+n1 > n1 + n2 OR n2 > n1 + n2
+What two positive numbers can make this possible:
+2147483647
+2147483647
+You entered 2147483647 and 2147483647
+You have an integer overflow
+YOUR FLAG IS: picoCTF{Tw0_Sum_Integer_Bu773R_0v3rfl0w_fe14e9e9}