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.
npx skills add mtarcure/claude-vibe-squad --skill erc1271-revert-data-checkgit clone --depth 1 https://github.com/mtarcure/claude-vibe-squadWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/mtarcure/claude-vibe-squad/erc1271-revert-data-check)<a href="https://agentmods.dev/skills/mtarcure/claude-vibe-squad/erc1271-revert-data-check"><img src="https://agentmods.dev/badge/skills/mtarcure/claude-vibe-squad/erc1271-revert-data-check/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/mtarcure/claude-vibe-squad/erc1271-revert-data-check"><img src="https://agentmods.dev/badge/skills/mtarcure/claude-vibe-squad/erc1271-revert-data-check.svg" alt="Reviewed on agentmods" width="80" height="20"></a>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.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00081 | $0.00709 |
| Opus 5.5 | $0.00032 | $0.00284 |
| Sonnet 5.5 | $0.00016 | $0.00142 |
| Haiku 4.5 | $0.00008 | $0.00071 |
Grade A, and why
erc1271-revert-data-check 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 1mo 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.
How it starts
The opening of the file, as written. The whole thing — 43 lines — stays where its author put it; the contents beside it link to each section on GitHub.
ERC-1271 Revert-Data Confusion Check
Audit smart-contract-wallet signature validation for the "revert-data trick": a low-level
staticcall/call to isValidSignature(hash,sig) whose EVM success flag is ignored, so an
attacker-deployed verifier that reverts with the ERC-1271 magic value (0x1626ba7e) in its
revert reason is misread as a valid signature — authorizing a drain.
Source: corpus A §I.3 — ChainSecurity / Zodiac Roles Modifier / Gnosis Pay, June 2026 (~$1.5M).
Impact class: funds theft / full wallet drain (intrinsic — clears the impact bar).
Governing method: a Phase-3a hypothesis lane of systematic-attacking; emits a lead only —
it re-enters the Phase 4–8 verification spine (runnable PoC on a mainnet fork, negative control,
G1–G4, cross-family repro) before it is ever a finding.
Method
- Grep the target for every ERC-1271 consumer:
isValidSignature, the0x1626ba7emagic value, and low-levelstaticcall/callinto a signer address (slither,semgrepcustom rule,castfor on-chain bytecode). - For each call site, confirm the code checks the call's success boolean BEFORE decoding
returnData. The bug pattern is(, bytes memory ret) = signer.staticcall(...)followed byret[:4] == MAGICwith the success flag discarded, or anassembly { returndatacopy }that never checkssuccess. - Build the differential PoC in Foundry: deploy a malicious verifier that
reverts withabi.encode(0x1626ba7e)(or raw bytes) in its reason; call the target's auth path with it as the declared signer. forgetest on ananvil --forkof the real deployment: assert the drain succeeds against the live contract state, then assert a success-checked reference implementation rejects it (link-level negative control).- Add a
halmos/forgeinvariant: "no auth path accepts a signature whose verifier call returnedsuccess == false."
Acceptance
- Every ERC-1271 / low-level-signer call site is enumerated with its success-flag handling classified.
- The PoC drains against a real mainnet fork, not a mock, and the negative control (success-checked variant) rejects the same input.
- Finding names the exact call site, the ignored success flag, and the realized fund impact; it is deduped against prior Zodiac/ERC-1271 disclosures before submission.
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.
- 1mo ago First seen · 43 lines · 81 tokens per session scan A b09695cfb103
erc1271-revert-data-check is a skill published in the GitHub repository mtarcure/claude-vibe-squad (165 stars, last pushed 1mo ago), licensed MIT. It adds 81 tokens to every session and 709 once invoked, about $0.0003 per session on Opus 5.5. 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 2026-09-19.
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