Day 9 — Runtime Threat Detection (The Shadow with Red Eyes)

Source: Dev.to

Runtime Threat Detection (The Shadow with Red Eyes)

The first CVE attack and runtime detection.
Black Forest Shadow is an ongoing Advent series exploring container security concepts through a dark fairy‑tale narrative.

Night settles heavily between the pines as Gord and Rothütle push deeper into the forest. Their two lanterns float in the dark like small wandering stars. The path narrows; frost crackles underfoot. A sudden crack of motion—

Rothütle’s lantern explodes in a burst of glass and darkness. He stumbles back, heart pounding.

“Who’s there?!”

Silence. Only the cold breath of the forest.

Gord is already beside him, her own lantern lifted. Its light casts Rothütle’s shadow long across the trunk of an ancient fir. Then the forest shifts. Gord lowers the lantern under her cloak, but the shadow on the tree remains, and now its eyes glow a burning red.

“Move away from the tree,” Gord whispers.

Rothütle tries. The shadow grabs his arm. Cold fingers of smoke coil around his sleeve, pulling him toward the bark. Gord lunges, sword flashing. The blade slices cleanly through the shadow’s arm—and a dark, wispy hand falls to the ground like spilled ink. Her next strike passes straight through the creature, as if it were made only of cloud and hate.

“It’s shifting!” Gord snaps. “I can’t hit it like this!”

Rothütle tears Gord’s cloak aside, exposing her lantern fully. A surge of light spills across the tree. The shadow shrieks—silent but violent—its edges dissolving. Now solid enough, Gord steps in, pivots, and with one precise swing she severs its head. The darkness collapses into nothing. The forest exhales.

Rothütle rubs his arm. Gord nods grimly.

“He wasn’t the talkative type.”

“So… you knew him?” Rothütle asks.

Gord inspects the fallen shadow.

“It’s a CVE,” she says flatly. “A Corrupting Vile Entity.”

Rothütle blinks.

“That explanation somehow made everything less clear.”

Tip of the Day: Detect threats at runtime — before they become breaches

The CVE in the forest behaves like a real‑world runtime threat:

• It hides in the dark (low‑visibility processes).
• It moves only when the system weakens (a lantern breaks).
• It becomes “solid” when illuminated — when observability reveals its behavior.

Modern workloads need the same protection:

• eBPF‑based monitors (e.g., Tetragon, Falco)
• Anomaly detection in Kubernetes
• Syscall tracing
• Real‑time policy enforcement

Like Gord exposing the shadow with a lantern, runtime detection exposes malicious behavior that hides in normal logs. Illuminate the threat → enforce policies → eliminate the danger.

Example: Falco detecting unexpected shell execution

# Falco rule: Unexpected Shell
- rule: Unexpected Shell
  desc: Container launched a shell unexpectedly
  condition: >
    spawned_process and container and
    proc.name in (bash, sh, zsh)
  output: >
    Unexpected shell in container (user=%user.name command=%proc.cmdline)
  priority: WARNING

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