L4 URG

TCP URG flood

Urgent pointer flag floods and URG-heavy combo presets. Legacy stacks and deep inspection engines may handle URG differently than modern Linux.

How it works

  1. Standalone preset: URG Flood (flag URG, invalid_flag true).
  2. Many combos in the library start with URG (UA, US, UARS, UAPRSF, etc.).
  3. Tests urgent-pointer parsing paths rarely exercised by production traffic.

Packet flow (illustrative)

TCP segments with URG flag or URG-inclusive combos.

Illustrative flow — not a live capture.

Base preset URG Flood
Related UA, US, UAPRSF…
Layer L4

What to watch in Engarde

  • Out-of-band handling differences across OS versions.
  • IPS CPU when URG combos match legacy rules.

Running this simulation

Start with URG Flood preset, then spot-check one URG combo (e.g. URG-ACK Flood) from the catalog.

Mitigation perspective

Modern best practice is often to strip or drop URG; confirm with simulation on your appliance OS.