Peculiar Internet Noteworthy Gizmo 1

NETWORK

Description

The network was dead quiet. Yet, in the eerie silence, I could almost feel the netadmin's presence, their thoughts and intentions woven into the very fabric of the IPAM.

Note: nmap is allowed INSIDE the instance.

The flag is NOT in standard format!

Hint

The internal hosts only respond to ping, no ports are open

Solution

The mention to IPAM should point in the direction of analyzing IP addresses. Moreover, the acronym of the title is ping.

Checking the available network interfaces (with e.g. ip a) reveals a chall interface:

2: chall: <BROADCAST,NOARP,UP,LOWER_UP> mtu 1500 qdisc noqueue state UNKNOWN group default qlen 1000
    link/ether ce:22:7c:6f:80:a7 brd ff:ff:ff:ff:ff:ff
    inet 10.10.0.1/23 scope global chall
      valid_lft forever preferred_lft forever

Since nmap is allowed a ping scan can be performed: nmap -sn -n 10.10.0.0/23.

The result of this scan shows that some hosts (133 out of 512) are up. Also, some kind of (possibly binary) pattern can be seen in the output: only two hosts (the 0.1 and the 0.2) do not fit well in it.

Plotting the hosts on the terminal could prove useful:

_XX____________________________________________________________________________________________________________________X_X_X____XXX_X____X_XXX____XXX_X_XXX____X____XXX_X_XXX_X____XXX____X_X_XXX_X____XXX_X_X_X____X____X____X_XXX_XXX_X____XXX_X_X_X____XXX_XXX_XXX____XXX_XXX_XXX____X_XXX_XXX_X____XXX_XXX____XXX_XXX_XXX____X_XXX_X____X_X_X____X____XXX_X_XXX_X____XXX_XXX_XXX____XXX_X_X____X____________________________________________________________________________________________________________________________

It seems like there are some blocks of either one or three consecutive hosts up. Moreover, the spaces between these blocks are also of one or four hosts down. This seems like Morse code, where X is a dot, XXX is a dash, _ is an intra-character gap and ____ is an inter-character gap.

Parsing the string this way leads to the flag:

... -. .- -.- . -.-. - ..-. -... . . .--. -... --- --- .--. -- --- .-. ... . -.-. --- -.. .
SNAKECTFBEEPBOOPMORSECODE

Solver

data = """
Nmap scan report for 10.10.0.1
Nmap scan report for 10.10.0.2
Nmap scan report for 10.10.0.119
[...]
Nmap scan report for 10.10.1.131
"""

data = [d[len("Nmap scan report for 10.10.") :] for d in data.split("\n")[1:-1]]
data = [d.split(".") for d in data]
data = [(int(a) << 8) + int(b) for [a, b] in data]

print(data)

dmap = [" " for _ in range(512)]

for d in data:
    dmap[d] = "X"

dmap = "".join(dmap)

print(dmap + "a")

dmap = dmap.replace("XXX", "-")
dmap = dmap.replace("X", ".")
dmap = dmap.replace("   ", "A")
dmap = dmap.replace(" ", "")
dmap = dmap.replace("A", " ")

print(dmap)