contracts-bridge-exploit

contracts-bridge-exploit is a skill for Claude Code from PurpleAILAB/Decepticon. It costs 64 tokens per session (1,350 once invoked), scanned A, original, Apache-2.0.

A Web3 security playbook for finding ways to forge, replay, or bypass messages that move assets between blockchains.

In plain words
What is it for?
It is for reviewing lock-and-mint, burn-and-redeem, optimistic, light-client, zero-knowledge, and liquidity-network bridges.
Why use it?
It helps expose weaknesses in validator signatures, bridge claims, Merkle proofs, token redemption, and cross-chain message validation.

Skill for Claude Code

Written for Claude Code: allowed-tools in frontmatter.

Good fit It is for reviewing lock-and-mint, burn-and-redeem, optimistic, light-client, zero-knowledge, and liquidity-network bridges.

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Install with agentmods
npx agentmods add skills/purpleailab/decepticon/bridge-exploit
About the project

Decepticon is an autonomous red-team agent that coordinates AI agents, security tools, sandboxes, and supporting services for authorized cybersecurity assessments. Security researchers and red teams can run it through its Docker stack, cloud service, command-line interface, or Python SDK, with the catalogue entries representing its available skills.

PurpleAILAB/Decepticon · 5,491 stars · on GitHub · decepticon.red

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

Any agent
npx skills add PurpleAILAB/Decepticon --skill bridge-exploit
Clone the repo
git clone --depth 1 https://github.com/PurpleAILAB/Decepticon

Made for: Claude Code.

Wrote this? Show the measurements

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README.md
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Per session 64 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,350 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe. Third-party audits
  • NVIDIA SkillSpector pass 7 Sept 2026
How audits are shown
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5.1 $0.00064 $0.01350
Opus 5 $0.00032 $0.00675
Sonnet 5 $0.00013 $0.00270
Haiku 4.5 $0.00006 $0.00135

Measured 9d ago against content hash 8e9ba92bace1, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-12, from the pricing page.

Security

Grade A, and why

contracts-bridge-exploit scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 9d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

Origin

Copies of this mod

1 near-identical copy found in the catalogue:

packages/decepticon/decepticon/skills/standard/contracts/bridge-exploit/SKILL.md · 115 lines

How it starts

The opening of the file, as written. The whole thing — 115 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Cross-Chain Bridge Attack

Bridges hold large pooled assets and execute messages from a separate trust layer. Architecturally fragile.

Bridge taxonomy

Type Trust model Past exploits
Lock-and-mint Trusted validators sign mint events Wormhole ($325M), Ronin ($600M), Harmony ($100M)
Burn-and-redeem Same Multichain/Anyswap ($126M)
Optimistic Fraud proof window Nomad ($190M)
Light-client / zk Cryptographic (Fewer hacks, but newer)
Liquidity-network (Hop, Connext) Routers + relayers Smaller individual exploits

Attack classes

1. Validator-signature bypass (Wormhole, Feb 2022, $325M)

The Solana-side verify_signature function trusted the caller to provide a "verified" sigset account. Attacker passed a sysvar that wasn't a real sigset → unauthorized mint of 120k wETH.

Lesson: any verify function whose input is a struct fetched by address is bypassable if address-trust is missing.

2. Validator key compromise (Ronin, March 2022, $600M)

9-of-9 validators, 5 of which were operated by one entity. Sky Mavis got phished → attacker controlled 5 keys → arbitrary mint.

Lesson: validator decentralization isn't math, it's operational. Count distinct legal entities and key-storage methods, not just keys.

3. Merkle-proof forgery (Nomad, August 2022, $190M)

After an upgrade, the zero-hash was set as a "valid root" — any proof against root = 0 passed. The first attacker withdrew real funds; then thousands of others copy-pasted the same tx with their own address. ~$190M total.

Lesson: check initialize / upgrade scripts for accidental defaults — bytes32(0), address(0), 1 (often the most-tested value) becoming the trusted value.

4. Replay across chains (Multichain class)

Bridge tx signed for chain A is replayed on chain B because chainId wasn't bound into the signed message:

function claim(bytes32 nonce, uint256 amount, bytes calldata sig) external {
    bytes32 hash = keccak256(abi.encode(nonce, msg.sender, amount));   // ⚠ no chainId
    require(ecrecover(hash, ...) == validator);
    token.transfer(msg.sender, amount);
}
// On chain A: legit claim
// On chain B (same validator, same token): replay the same sig

Read the full file on GitHub · 115 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 9d ago First seen · 115 lines · 64 tokens per session scan A 8e9ba92bace1

Subscribe to this mod's changes

contracts-bridge-exploit is a skill published in the GitHub repository PurpleAILAB/Decepticon (5,491 stars, last pushed 13d ago), licensed Apache-2.0. It adds 64 tokens to every session and 1,350 once invoked, about $0.0003 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-09-03.