L4 APRSF

TCP ACK-PSH-RST-SYN-FIN flood

Five-flag combo preset (APRSF) — maximum “everything set” handshake chaos for parser and IPS regression testing.

How it works

  1. Engarde preset: ACK-PSH-RST-SYN-FIN Flood — flag APRSF, invalid_flag true.
  2. Represents worst-case flag surface in a single segment class.
  3. Use after baseline single-flag tests to find IPS rule gaps.

Packet flow (illustrative)

Segment with ACK+PSH+RST+SYN+FIN flags (APRSF).

Illustrative flow — not a live capture.

Flags A+P+R+S+F
Engarde APRSF preset
Use case IPS regression

What to watch in Engarde

  • Alert vs. drop behavior on each protection tier.
  • Compare with UAPRSF (adds URG) for incremental diff.

Running this simulation

Lab-only short run of APRSF preset; document which device first drops or alerts.

Mitigation perspective

Explicit deny for multi-flag anomalies; never assume “will never happen in prod”.