CSE545_SS_Work/Dojo Notes.md

CSE 545 - Fall '24 pwn.college Dojo

Project 01 Linux Lifter

.05 - find

• find / randomly_placed_file - way too many files
• read the man page. find -name randomly_placed_file found it
• didn't specify a folder to search in tho, ig it's cuz cwd is /

.06 - find and exec

• "Optional Exercise: Why do they think it worked with -exec parameter of the find command, but we get permission denied using standalone cat command? Hint: SUID bit was set for the find command."
• indeed, we see that /usr/bin/find has its setuid bit set:
• see here for find stuff
• find / -name random_cant_flag -exec cat {} ';' worked

.07 - return code

• $? is the return code of the last executed command
• range 0 to 255

.08 - python

• SUID on python this time

.11 - search me

• /challenge/tester.sh is printing /flag but the file is missing
• /challenge/cp has SUID bit set
• preliminary find revealed a possible file deep in /tmp
• find /tmp/that/full/path -name flag -exec /challenge/cp {} /flag ';'

.12 - hash it out

• used online tool to generate SHA256

.13 - hash full

• here we go
• a-z, 6 spaces, so 26^6 possibilities
• plaintext is 6 letters, so 48 bits. hash is SHA256 so 256 bits.
• storage per line:<hash><plaintext> that's 304 bits, 312 if including newline character
• total storage exceeds 11GB!!
• refinement 1: 256-bit hash is pretty unique. if we cut down on the portion of the hash stored, we should be able to save a ton of space while only slightly increasing the margin of error. let's assume plaintext has to be stored entirely for now, so total per line is 184 bits.
• eh fk it, just generated all permutations. 22GB storage, 20 min to generate, search using VSCode search took a few more minutes

Project 02 Unwinding Binaries (Reversing)

.01 - looking inside

• not sure how to use ghidra, didn't seem to work either
• angr decompile /challenge/run revealed a strcmp with the key, ez

.02 - the mangler

• 'mangling' is just subtracting 3 from the char's ascii value. so just add 3 to the key

.03 - XOR plus

• mangling is adding 3 then XOR with 2. so just XOR with 2, then subtract 3

lab 2a.02

• ascii values

.04 - solve for x

• NOTE: angr screwed up, and gave an incorrect result (== instead of !=)
• use ghidra (GUI) or dogbolt for binaries under 2MB
• anyway, math solving:
  • we get a few eqns:
    • v1 = v0 - 24223
    • v3 = 5v2 - 129519
  • use these eqns to reduce from brute-force 4 nested loops to 2 nested loops
  • then verifying the rest gets us one soln
• runtime < 3 seconds

.05 - extra verification

• angr just straight up hangs lol
• holy sh*t so many if statements
• boils down to byte by byte, check 1 or 0, check +ve or -ve (MSB)
  • 00 - 00110111
  • 01 - 01000111
  • 02 - 01000011
  • 03 - 01010110
  • 04 - 00110100
  • 05 - 01010010
  • 06 - 01011010
  • 07 - 01001001
  • 08 - 01000001
  • 09 - 00110100
  • 10 - 01011001
  • 11 - 00111000
  • 12 - 01111001
  • 13 - 00110011
  • 14 - 01110011
  • 15 - 01001000
  • 16 - 00110101
  • 17 - 00111000
  • 18 - 01101010
  • 19 - 01010111 (binary ninja and hex-rays disagreed on this, binary ninja was right)
• could have automated this smh

.06 - extra verification II

• first ordered all if statements to get bitwise order of the string (hell.)
• for result to be 0 at the end, just don't modify it at all
• so for each if statement, check which of 0/1 makes it false (find and replace ftw)
• ascii string is 67kW6YnKvTpaqoBX1F8l
• really should have automated this

.07 - binary labyrinth

• omg it's literally labyrinth navigation, using wasd keys LMFAO

int M[12][12]={
  { 1, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1},
  { 1, 0, 1, 0, 0, 1, 0, 1, 0, 0, 0, 0},
  { 1, 0, 0, 0, 1, 1, 0, 1, 0, 1, 0, 1},
  { 1, 0, 1, 0, 1, 1, 0, 1, 0, 0, 0, 1},
  { 1, 0, 0, 0, 1, 0, 0, 1, 0, 0, 1, 1},
  { 1, 1, 0, 1, 1, 0, 0, 0, 0, 0, 1, 1},
  { 1, 1, 0, 1, 1, 0, 1, 1, 1, 0, 0, 1},
  { 1, 1, 0, 0, 0, 1, 1, 0, 0, 0, 1, 1},
  { 1, 1, 0, 1, 0, 1, 0, 0, 1, 1, 1, 1},
  { 1, 1, 0, 1, 0, 1, 1, 0, 1, 1, 1, 1},
  { 1, 1, 0, 1, 0, 0, 0, 0, 1, 1, 1, 1},
  { 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1}
};

• 1s are landmines
• start from row 1, column 2 (x=1, y=0)
• goal is row 2, column 12 (x=0xb, y=1)
• ssssdsssddsssdddwwwddwwwwdwwd
• lol

Project 03 Hacking Network Highways

.01 - netcat

nc 10.0.0.3 31337

.02 - netcat listener

nc -l 31337

.03 - nmap and netcat

nmap 10.0.0.0-255 # found in .142
nc 10.0.0.142 31337

.04 - nmap in parallel and netcat

• -sn for ARP ping scan - no ports just discover host
• --min-parallelism 10 for at least 10 probes at a time
• consider using -T4 or -T5 timing templates
• checked
  • 10.0.0.0/19 - only us at .2
  • 10.0.32.0/19 - nothing
  • 10.0.64.0/19 - 10.0.90.244 and port is 31337 as expected. stopped here

.05 - tcpdump

• tcpdump -A 'tcp port 31337'
  • -A to print content as ASCII

.06 - tcpdump and flow

• inspecting the /challenge/run python script, we see that it's sending one character at a time, after encoding them
• tcpdump -s 65535 -nntA 'tcp port 31337' -w /home/hacker/my_pcaps/3.06.pcap
  • -s to grab full packet (?)
  • -nn to avoid resolution of hostnames or port numbers
  • -t to exclude timestamp
  • -A to print content as parsable ASCII. important!!!
• then we use scapy to read the packets, skip alternating duplicates, decode, and form a single string
• ehh i messed up something but whatever

.07 - mimic and listen

• ip addr add 10.0.0.2 dev eth0 assign the address to us, fake
• nc -l 10.0.0.2 31337

.08 - ether scapy

• jfc
• ALWAYS be explicit and define the src addresses
• didn't define the src MAC addr, so packets kept going thru lo instead of eth0
• too stupid to realize it in time too
• anyway, get current MAC addr of eth0
• craft Ether packet to given dest addr with type 0xFFFF
• srp(pkt, iface='eth0')

lab 3a was chill, no notes

.09 - IP scapy

• similar
• set IP addr with ifconfig eth0 10.0.0.2
• add l3 with src and dest IP addr, proto=0xFF
• since we need MAC as well, use srp, not sr

.10 - TCP scapy

• similar
• again, set IP addr
• add l4 with src and dest TCP port, flags=0x1F to set ACK (0x10), PSH (0x08), RST (0x04), SYN (0x02), FIN (0x01) flags
• srp again

.11 - TCP handshake

• send SYN with specified seq and ack numbers - 31337 both
• get SYNACK
  • has ack of 31338, which will be our next syn
  • has random syn, add 1 to get next ack
• send ACK with next syn and ack numbers

.12 - ARP scapy

• meh, arp opcode is 2

.13 - ARP spoofing

• meh, just crafting ARP and tcpdump

lab 3b was chill, no notes

.14 - MiTM ARPing

• shit's getting too easy, let's not look at /challenge/run
• first, get target's macs, then arp spoof
• we don't have NET_ADMIN, so can't set ip_forward in sysctl to control MITM directly,
• first, capture packets, check raw loads
• we observe that a sequence repeats:
  • 10.0.0.3:31337 sends a command: "SECRET", to 10.0.0.4 at a random port
    • note: how does 3 know which port to send to?
      • [after 3d] idiot, 4 opens the tcp handshake
  • 4 responds with a secret, it's in ascii?
  • 3 sends a list of available (?) commands - echo, flag, and then asks for a command
  • 4 responds with echo, and sends "Hello, World!"
  • 3 echoes it back
• connection closes, repeats with another randomized port for 4
• note that 3 sends a secret and a list of commands that includes a flag command
• craft a packet masquerading as 4, with the flag command, wait for a secret to arrive and put it in the packet
  • [after 3d] idiot, read the code, you don't need the secret, just hijack the connection
• in the time it takes 3 to do the legitimate echo from 4, we could probably send the flag command to 3 and have it processed in the same ephemeral connection
• let's try

lab 3c was chill, no notes

lab 3d

.2 - mitm arping

• same as 3.14, approaching this first for deadline
• client at 3.13.37.4, random port
• server at 3.13.37.3, port 1992
• flow:
  • TCP handshake:
    • client -> SYN -> server
    • server -> SYNACK -> client
    • client -> ACK -> server
  • secret is sent:
    • server -> PUSHACK -> asks for secret -> client
    • client -> ACK, then PUSHACK -> secret string \n-> client
    • server -> ACK, then PUSHACK -> secret confirmed -> client
      • at this point, inject BACKDOOR packet before the actual client
    • client -> ACK, then PUSHACK -> ECHO: -> server
  • after backdoor, send a FLAG packet

going back to continue 3.14 with this understanding

---

• [after 3d] updated understanding
  • client at 10.0.0.4, random port
  • server at 10.0.0.3, port 31337
  • flow:
    • TCP handshake:
      • client -> SYN -> server
      • server -> SYNACK -> client
      • client -> ACK -> server
    • secret is sent:
      • server -> PUSHACK -> asks for secret -> client
      • client -> ACK, then PUSHACK -> secret string \n-> client
      • server -> ACK, then PUSHACK -> list of commands -> client
        • at this point, inject FLAG command before the actual client
      • client -> ACK, then PUSHACK -> ECHO -> server

Project 04 Hijacking Binary Power (Pwning)

• seems we have access to the source code, and we're given a suid-set executable

.02 - exec them all

• title helped
• exec -a <passwd> /challenge/run

.03 - altering arg[0]

• +3 lops off first 3 chars

.04 - symmer

• symlink /flag to ~/flag

.05 - when is a secret not secret

.10 - somewhere over the rainbow

• online tool

.11 - byte compare

• this strncmp takes the lower length (doesn't take null tho), so just give it a single byte
• only 256 possible values, bruteforce

for i in $(seq 0 255); do
  i_chr=$(printf "\x$(printf "%x" "$i")")
  /challenge/run $i_chr
done

.12 - symmer in time

• 5 second window
• initially have a dummy ~/flag, run the challenge, within 5 seconds delete it and create it as a symlink to /flag

.13 - time after time

• 2 second window
• creates tmp files, writes target to one, sleeps for 2 secs, then reads from it and compares with passwd checksum
• have umask 002 ; echo <checksum> > /tmp/hash_output_1000_<randnum> in one shell ready for tab completion of the random number part
• run /challenge/run something in another shell, then run the above

.14 - controlling your path

• make sure PATH is set so that it uses your program
• don't specify a shell so that it uses /bin/sh - see here

  "If the process image file isn't a valid executable object, the contents of the file are passed as standard input to a command interpreter conforming to the system() function. In this case, the command interpreter becomes the new process image."

• i assume the command interpreter that gets used has the SUID bit

.15 - blind leading the blind

• basically, stdout and stderr for the child are set to /dev/null so instead of spawning root shell, use cat flag > output and read output

.16 - arg wars VI - return of the hacker

• decompiler showed set of filtered characters, quotes and backslashes are not there
• also .17 checks for backslashes, so i assume backslashes solves this
• but i got stuck, TA said try the 'prequels' first then come back lol

lab 4a.1 - easy overflow

• standard buffer overflow vuln
• gdb shenanigans
• shift-ctrl-@ inserts a null character it seems (remember for .16)
• enough gdb, let's move to big guns - pwntools
• checksec says no stack canary or PIE
• all g then
• calculate offset from vulnerable variable location to saved RIP(return instruction pointer) location
• get address of target function to execute
• craft payload accordingly

lab 4b.1 - overflow + shellcoding 1

• buffer overflow vuln
• have to write and inject shellcode
• checksec says protections are disabled
• pwntools generated shellcode for /bin/sh:
  • push /bin/sh to stack, set ebx to this address
  • setting argv - push sh null-terminated (hv to use XOR trick to null-terminate, which isn't necessary for memcpy tho), set ecx to this address
  • setting env - XOR out edx
  • executing execve - syscall execve
• so
  • get shellcode on the stack
  • calc offset from rsp to start of shellcode
    • rsp is obtained at runtime, program outputs it
    • if we put shellcode in the vulnerable variable, we can use its location to store shellcode since its not being modified
    • and in this case, rsp=variable location cuz last variable on stack
  • add offset to rsp to get shellcode location
  • put that as target rip
  • padding in between
  • boom

lab 4b.2 - overflow + shellcoding 2

• ummm
• apparently the difference was replacing memcpy with strcpy
• memcpy doesn't care about null bytes, strcpy does
• but since i used robust shellcode from pwntools ahaha....
• it already took care of that
• so 4b.1 solution applied here too

.19 - pile on

• unsanitized input to system() - basic shell injection

.20 - | escape from cmd

• input escaped by double quotes
• just tried randomly, this worked to inject:

/challenge/run ';`lint`'

.21 - substitute commander

• checked for double quote in input, so prev soln worked here too

.22 - arg wars I - the phantom command

• find command
• injection vuln, only checks for semicolon
• so same works again, replace with &&

.23 - arg wars II - attack of the chars

• checks for dollar in addition (variable substitution)
• so same works again

.24 - arg wars III - revenge of the tick

• ah now the backtick has been filtered. but not the ampersand!

/challenge/run 'test && lint'

.25 - arg wars IV - a new hole

• now the source is not available, hv to decompile
• we see that now ampersand has been filtered out as well
• lets try quotes to have find do an exec

/challenge/run test" -exec /home/hacker/lint {} +"

.26 - arg wars V - the system strikes back

• pipe symbol now added to filter
• luckily we didn't use that

.27 - overflow gods

• buffer overflow vuln
• ^A is ASCII 1

.28 - the power of a god

• just overflow again, doesn't matter if stack or global var

.29 - direct is best

• we get direct access to set any value on stack - control flow vuln (lol)
• set saved rip to target function address

.30 - stack direct

• similar access. no source code
• decompiled, found a flag==0xcafebabe check to execute a root shell

.31 - data direct

• even more direct access - no addition of address, just direct address control (lol)
• set flag to 0xdeadfeed

lab 4b.3 - overflow + a defense

• similar to 4b.1 and 4b.2
• but here we dont have RSP so we cant point RIP to it
• instead there's a function that has jmp *%rsp
• so first, pad the vulnerable stack buffer upto the saved RIP's address
• put that function's address in it
• now, remember that when a function returns, it pops its stack
• so we need to put our shellcode after this saved RIP's location
• that way, when the current function returns into the target function, the target function's RSP will point to the shellcode
• boom

lab 4c.1 - rop

• buffer overflow vuln, but NX is enabled on stack
• ROP time
• we need:
  • location of a string "/bin/sh" in rdi (path)
  • 0 in rdx (argv)
  • 0 in rsi (envp)
  • 0x3b in rax (execve)
  • finally run syscall
• ASLR is enabled, but program gives us the address of libc
• from pwn, we have ROP(ELF(libc.so path)) to get ROP gadgets from libc
  • other tools exist, like ROPGadget.py, one_gadget, ropium
• find necessary gadgets and args
  • some might not exist in the exact form required, maybe some baggage is attached, or a roundabout way is needed (xor instead of directly loading, etc)
• boom