Survival Of The Fittest

Technical Walkthrough

Writeup

Challenge

• Name: Survival-of-the-Fittest
• Category: Blockchain
• Difficulty: Very Easy
• Mode: remote

Summary

The launcher exposed a funded private key, player address, setup address, target address, and RPC endpoint. The Creature contract is simpler than the previous boss challenge: it loses life directly on any attack and the solve path is simply to call strongAttack(20) to reduce lifePoints from 20 to 0, then call loot() to drain the target balance and satisfy Setup.isSolved().

Artifact Inventory

• analysis/connection_info.http — initial launcher credentials and addresses.
• analysis/connection_info-live.json — refreshed live credentials and addresses used for the final solve.
• analysis/extracted/blockchain_survival_of_the_fittest/Creature.sol — challenge contract source.
• analysis/extracted/blockchain_survival_of_the_fittest/Setup.sol — setup/win-condition source.
• analysis/solve-result.json — post-exploit chain state showing isSolved=true.
• analysis/flag-response.txt — raw flag response before harness capture.
• solve/solve.py — reproducible exploit.

Reference analysis/artifact-inventory.json and summarize the relevant files or remote surface.

Analysis

Setup.isSolved() returns true when the target contract balance reaches zero. Creature starts with lifePoints = 20, and strongAttack(uint256) directly subtracts the supplied damage through _dealDamage. There is no tx.origin trick or ownership gate here. Therefore a single strongAttack(20) call is sufficient to kill the creature, and loot() can then transfer the contract balance to the player.

Solve

The solver refreshes /connection_info at runtime to avoid stale launcher addresses, then uses web3 to call strongAttack(20) from the provided funded account, followed by loot(). After verifying Setup.isSolved(), it fetches /flag.

Flag

Raw flag is stored in loot/flag.txt and intentionally not reproduced here.

Lessons

Very Easy blockchain challenges can share the same launcher UI while differing dramatically in exploit complexity. Always read the current contract source instead of assuming the previous challenge pattern still applies. Here the entire puzzle collapsed to the win condition plus two direct transactions.

Source-Backed Dossier

The sections below are merged from companion Markdown notes for the same case. They are rendered after sanitization so the article stays precise without publishing raw flags, credentials, or target-specific secrets.

Notes

Scope

• Challenge: Survival-of-the-Fittest
• Category: Blockchain
• Difficulty: Very Easy
• Mode: remote
• Remote instance: <TARGET>:32288
• Start time: 2026-06-07T09:11:10Z
• Operator: harness
• State file: challenge-state.json

Harness Status

• Current phase: see challenge-state.json
• Next allowed actions: see next-action.json
• Raw flags and sensitive material stay in loot/ only. Do not paste them here.

Artifact Inventory

Evidence Ledger

Key Findings

-

RAG / Advisory Memory

RAG output is advisory only. Record evaluated retrievals with:

scripts/challenge_harness.py rag-record <workspace> --query "..." --tag MATCHED|PARTIAL|MISSING|<secret redacted>|GENERIC --validation "..."

Secrets/Flags

Raw flags and sensitive material stay in loot/ only. Use scripts/challenge_harness.py capture-flag to validate and record flag capture without printing the value.

Scenario

Alex had always dreamed of becoming a warrior, but she was not particularly skilled. When the opportunity arose to join a group of seasoned warriors on a quest to a mysterious island filled with real-life monsters, she hesitated. But the thought of facing down fearsome beasts and emerging victorious was too tempting to resist, and she reluctantly agreed to join the group. As they made their way through the dense, overgrown forests of the island, Alex kept her senses sharp, always alert for the slightest sign of danger. But as she crept through the underbrush, sword drawn and ready, she was startled by a sudden movement ahead of her. She froze, heart pounding in her chest as she realized that she was face to face with her first monster.

Operator Question

Analyze the provided Blockchain challenge artifact and live target host, identify the smart contract or blockchain interaction required, exploit or solve it reproducibly, and capture the HTB flag.

Memory Summary

Metadata

• Platform: HackTheBox Challenges
• Category: Blockchain
• Challenge: Survival-of-the-Fittest
• Difficulty: Very Easy
• Source workspace: <local workspace>

Validated Solve Chain

Concepts only. Do not include raw flags, reusable credentials, tokens, cookies, private keys, or live secrets.

1.

Reusable Lessons

-

Dead Ends

-

Tool Quirks

-

Evidence Paths

-

Ingestion Decision

• Proposed for LightRAG: yes/no
• Requires user approval before ingestion: yes

Hypothesis Board

Keep no more than 3 active hypotheses on Easy/Medium and 5 on Hard unless the user explicitly asks for breadth.

Closed Branches

Memory Summary

approval_required: true

Sanitized Memory Summary

Metadata

• Platform: HackTheBox Challenges
• Category: Blockchain
• Challenge: Survival-of-the-Fittest
• Difficulty: Very Easy
• Source workspace: <local workspace>

Validated Solve Chain

Concepts only. Do not include raw flags, reusable credentials, tokens, cookies, private keys, or live secrets.

1.

Reusable Lessons

-

Dead Ends

-

Tool Quirks

-

Evidence Paths

-

Ingestion Decision

• Proposed for LightRAG: yes/no
• Requires user approval before ingestion: yes

Notes

Notes

Scope

• Challenge: Survival-of-the-Fittest
• Category: Blockchain
• Difficulty: Very Easy
• Mode: remote
• Remote instance: <TARGET>:32288
• Start time: 2026-06-07T09:11:10Z
• Operator: harness
• State file: challenge-state.json

Harness Status

• Current phase: see challenge-state.json
• Next allowed actions: see next-action.json
• Raw flags and sensitive material stay in loot/ only. Do not paste them here.

Artifact Inventory

Evidence Ledger

Key Findings

-

RAG / Advisory Memory

RAG output is advisory only. Record evaluated retrievals with:

scripts/challenge_harness.py rag-record <workspace> --query "..." --tag MATCHED|PARTIAL|MISSING|<secret redacted>|GENERIC --validation "..."

Secrets/Flags

Raw flags and sensitive material stay in loot/ only. Use scripts/challenge_harness.py capture-flag to validate and record flag capture without printing the value.

Scenario

Alex had always dreamed of becoming a warrior, but she was not particularly skilled. When the opportunity arose to join a group of seasoned warriors on a quest to a mysterious island filled with real-life monsters, she hesitated. But the thought of facing down fearsome beasts and emerging victorious was too tempting to resist, and she reluctantly agreed to join the group. As they made their way through the dense, overgrown forests of the island, Alex kept her senses sharp, always alert for the slightest sign of danger. But as she crept through the underbrush, sword drawn and ready, she was startled by a sudden movement ahead of her. She froze, heart pounding in her chest as she realized that she was face to face with her first monster.

Operator Question

Analyze the provided Blockchain challenge artifact and live target host, identify the smart contract or blockchain interaction required, exploit or solve it reproducibly, and capture the HTB flag.