A practical defender-focused guide that explains how to detect steganography and covert channels across files, hosts, and networks. It covers file- and behavior-level signals, network indicators, detection techniques and tools, example analytic rules, an incident playbook, and practical takeaways for building layered detection.
Steganalysis and Detection Signals — Finding the Hidden Stuff "Steganography is the art of whispering in a crowded room. Steganalysis is yelling, listening to the echoes, and noticing the person who keeps oddly chewing gum." — Your friendly, slightly manic TA
You already learned the what and why of steganography in System Hacking: Covert Operations and Persistence (we covered common carriers, LSB tricks, and why attackers love images and benign documents). You also studied EDR-aware tradecraft and hardening strategies. Now we flip the script: how do def...
Why detection is a different beast Attackers can hide payloads in mundane files (images, audio, MS Office docs) and in seemingly normal network flows (DNS, HTTP, timing channels). Many stego techniques look benign at first glance. You won't always see a binary that screams "malware.&qu...
The core detection signals (what to look for) 1) File-level signals Unusual entropy patterns : stego payloads (especially encrypted/compressed) increase entropy in parts of a carrier. Look for images with segments of unexpectedly high entropy. Embedding artifacts : LSB changes, color distribu...
2) Filesystem and process behavior signals Odd read/write patterns : carriers altered only at odd times, or by processes that normally wouldn't modify media files (e.g., a service account process editing images). Persistence via stego : hidden payload extracted at runtime and executed — wat...
3) Network signals DNS tunneling and payload-in-DNS : long query names, high entropy labels, or suspicious base32/base64-looking tokens in subdomains. HTTP image uploads/downloads : repeated GET/POSTs of images with small differences; transfers at odd intervals. Timing/padding channels : regu...
Detection techniques and tools (practical) Technique Signal type Strengths Weaknesses Statistical/Lossless entropy analysis File Good for encrypted payloads False positives on compressed files Structural/transform analysis (DCT/FFT) Images/audio Targets LSB and frequency dom...
Example analytic rules (starter recipes) YARA-like idea (concept): flag PNGs with abnormal entropy in the IDAT chunk. Sigma/Suricata-style hunting ideas: Alert on processes that read image/doc files then spawn a shell or create a memory-mapped executable. Alert on DNS queries with label ent...
False positives and adversary tricks — be realistic Cameras, modern encoders, and legitimate compression often produce high entropy. Don't ban all high-entropy files; correlate. Attackers can use cover traffic, mimic normal upload patterns, or use multi-stage embedding to reduce signals. ...
Incident playbook (short) Triage: collect the carrier file(s), network captures, host timelines, and process memory dumps. Static checks: exiftool, entropy scan, binwalk, and steg tools (zsteg, steghide). Document hashes. Memory analysis: search for extracted payloads, suspicious PE/ELF heade...
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