Forensics CTF Methodology: What to Look For and Where

At DEF CON 2025, a forensics challenge called DeadDrop stumped hundreds of teams for 18 hours. The flag was sitting in a deleted registry hive, recoverable in under three minutes with the right approach. Most teams never looked there because they had no methodology — they were guessing. This post gives you the systematic process that finds flags fast.

Step 1: Triage the Evidence Before You Touch Anything

Your first two minutes on any forensics challenge should be pure reconnaissance. Know what you have before you start digging. Jumping straight into Autopsy or Volatility without understanding the artifact type wastes time and hides the obvious.

Start with file and binwalk on every artifact. file identifies the true format regardless of extension. binwalk scans for embedded files and known signatures inside a blob — a JPEG might have a ZIP hiding at offset 0x4A2F.

$ file challenge.img
challenge.img: DOS/MBR boot sector; partition 1: ID=0x83, active, start-CHS (0x0,2,3), end-CHS ...

$ binwalk challenge.img
DECIMAL       HEXADECIMAL     DESCRIPTION
--------      -----------     -----------
0             0x0             MBR boot sector
512           0x200           Linux EXT4 filesystem
104857600     0x6400000       Zip archive data, at least v2.0 to extract
104858112     0x6400200       End of Zip archive

That output tells you two things immediately. You have an EXT4 partition to mount and an unexpected ZIP archive embedded at offset 104857600. The ZIP is almost certainly not accidental — that is your first lead. Extract it with binwalk -e challenge.img and examine the ZIP contents before you even mount the filesystem. Many teams waste an hour on the filesystem while the flag is sitting in the embedded archive.

After triage, note file sizes, timestamps, and any strings that look out of place. Run strings challenge.img | grep -iE 'flag|ctf|key|pass' as a quick sanity check. It finds low-hanging fruit before you commit to deep analysis.

Step 2: Filesystem Analysis — Deleted Files Are Your Best Friends

Mounted filesystems show you what the OS wants you to see. Forensic tools show you everything else. For CTF disk images, deleted files and unallocated space are where challenge authors hide flags because most beginners never look there.

Mount the image read-only first, then run fls from The Sleuth Kit — a command-line toolkit for filesystem forensics — to list all files including deleted ones. Deleted entries show an asterisk prefix.

$ sudo mount -o ro,loop,offset=512 challenge.img /mnt/ctf

$ fls -r -d /dev/loop0
r/r * 14: home/jdoe/.bash_history
r/r * 27: home/jdoe/.ssh/id_rsa
r/r * 31: tmp/transfer_20260814.zip
d/d * 44: var/log/audit

Every starred entry is deleted but still recoverable. That id_rsa at inode 27 and transfer_20260814.zip at inode 31 are obvious targets. Use icat to recover them by inode number — icat /dev/loop0 27 > recovered_id_rsa. Check recovered_id_rsa for embedded text or use it to decrypt another artifact in the challenge. Deleted bash history at inode 14 often contains the exact commands an attacker ran, which can point you directly to the flag location.

Also check unallocated space with blkls /dev/loop0 | strings | grep -i flag. Challenge authors sometimes write flags directly to slack space between file blocks.

Step 3: Memory Dumps — Process Trees and Network Artifacts

Memory forensics challenges almost always involve a .raw, .vmem, or .mem dump. Volatility 3 is your primary tool here. It reconstructs running processes, open network connections, and loaded DLLs from raw RAM snapshots.

Start with the process tree and network connections. Anomalies in either one point you to the malicious process — and its memory often contains the flag string directly.

$ vol3 -f memdump.raw windows.pstree
PID   PPID  ImageFileName         Offset
4     0     System                0x82341040
392   4     smss.exe              0x8a12f040
512   392   csrss.exe             0x8b023040
644   392   winlogon.exe          0x8c341040
1284  644   explorer.exe          0x8f210040
2048  1284  cmd.exe               0x9a100040
2112  2048  powershell.exe        0x9b200040  <-- suspicious
2304  2112  nc.exe                0x9c100040  <-- netcat child

$ vol3 -f memdump.raw windows.netstat
Offset   Proto  LocalAddr          ForeignAddr         State
0x9c1..  TCPv4  192.0.2.47:49231   192.0.2.200:4444    ESTABLISHED

A powershell.exe spawning nc.exe with an established connection to 192.0.2.200:4444 is a textbook reverse shell. Dump that process memory with vol3 -f memdump.raw windows.memmap --pid 2112 --dump then run strings on the output. Challenge flags are often sitting in the process heap as plaintext because the script that fetched or generated the flag was still running when the dump was taken.

Also run windows.cmdline to see exactly what command launched each suspicious process. Encoded PowerShell base64 arguments are common — decode them with echo '<base64>' | base64 -d and you frequently find the flag or the path to it.

What To Do Now

Download the retired forensics challenge Reminiscent from HackTheBox and work through it using this exact sequence: triage with file and binwalk, then Volatility for the memory component. Time yourself. If you finish in under 30 minutes, your methodology is solid. If not, note exactly where you stalled — that gap is your training target for next week.