Vyper-specific detection

Why a separate skill

Vyper has different defaults than Solidity. Some patterns that are safe in Solidity are unsafe in Vyper, and vice versa. Vyper has also had compiler-level reentrancy bugs (most famously the 2023 Curve incident). Audit Vyper with Vyper-aware eyes.

When this applies

• Any .vy file
• Any # @version pragma directive
• Any contract using raw_call, send, selfdestruct, create_forwarder_to
• LP tokens, AMM pools written in Vyper (Curve and forks)

Detection patterns

Compiler-version reentrancy bug (CRITICAL)

Vyper 0.2.15 / 0.2.16 / 0.3.0 had a broken @nonreentrant lock — the lock was per-key, but the same key was reused across functions, causing locks to fail to engage in some compositions. Caused the Curve / Vyper exploit (July 2023, ~$73M).

Action: any contract pinned to # @version 0.2.15, 0.2.16, or 0.3.0 — treat reentrancy guards as broken. Recommend upgrade to ≥ 0.3.7 (or 0.3.10+ for ongoing support).

# @version 0.2.15        # ← FLAG: known-broken nonreentrant

raw_call ignores return data unless max_outsize set (HIGH)

raw_call(target, b"...")    # ← return data ignored entirely

Default revert_on_failure=True will revert the calling tx on a revert, but the return data is silently dropped. If you need to read the return:

ok: bool = raw_call(target, b"...", max_outsize=32, revert_on_failure=False)

send forwards 2300 gas (HIGH on L2s)

Same problem as Solidity transfer. Smart-wallet recipients can't receive. On L2s with different base costs (Berachain, etc.), the 2300 gas bound is unreliable.

Use raw_call(addr, b"", value=amount) with explicit gas bounds.

default_value= on storage (MEDIUM)

HashMap[address, uint256] defaults to 0 for unset keys. Vyper devs sometimes assume "exists vs not-exists" semantics that don't apply. Use a paired bool flag if existence matters.

selfdestruct semantics (HIGH on pre-Cancun)

Same EIP-6780 caveats apply ([[selfdestruct-eip6780]]). Vyper code that relies on selfdestruct deleting code is broken post-Cancun on mainnet (March 2024).

create_forwarder_to clones share code (HIGH)

EIP-1167 minimal-proxy clones via create_forwarder_to. Same gotcha as Solidity: per-clone init guard required, or anyone can initialize a fresh clone.

Decimal scaling (MEDIUM-HIGH)

Vyper's decimal type is fixed-point with limited range. Mixing uint256 and decimal for price math invites overflow or precision loss. Most modern Vyper code avoids decimal; if present, audit carefully.

external vs internal and visibility (MEDIUM)

Vyper enforces explicit visibility (@external, @internal, @view, @pure). Functions without visibility are syntax errors — but @external + missing access checks are still a foot-gun (same as Solidity).

msg.sender == self patterns (MEDIUM)

Vyper allows msg.sender == self checks — used to gate "callable only from internal call". Easy to typo msg.sender == self.owner vs == self. Check the intent.

assert vs raise (LOW)

assert and raise both revert. assert <cond> reverts if false; raise "reason" always reverts. Mix-up on devs coming from Solidity. Both are safe; just consistency.

Storage layout — Vyper has no __gap convention (HIGH for upgradeable)

Vyper isn't typically used for upgradeable contracts (no equivalent of OZ Upgradeable plugin). If you find a Vyper proxy implementation, audit storage layout very carefully — reserved slots aren't a Vyper convention.

Severity rubric

Remediation patterns

• Upgrade to Vyper ≥ 0.3.10 to get fixed @nonreentrant.
• Use raw_call with explicit max_outsize + check return.
• Replace send with raw_call(addr, b"", value=amt) and explicit gas budget.
• Use OZ ReentrancyGuard-equivalent only after verifying the compiler version.
• For Curve forks specifically: pin compiler, audit the lock implementation against the Curve patch commits.

False-positive notes

• Vyper test fixtures often use @version 0.2.x for legacy compatibility — verify deployment compiler differs.
• Curve LP tokens and pools have been re-audited extensively; current Curve deploys use post-fix Vyper.

Related

• [[reentrancy]] — base reentrancy patterns
• [[selfdestruct-eip6780]] — EIP-6780 implications
• [[unchecked-calls]] — raw_call analog of low-level call

Compiler-Specific Notes (v0.4+)

When analyzing Vyper contracts compiled with v0.4+, the @nonreentrant decorator uses a mutex storage slot. Reentrancy guards that rely on storage checks between external calls MUST account for Vyper's 0-indexed mutex storage layout (sload(0) vs sload(keccak256)).

Detection Path: external call → state mutation → nonreentrant check bypass

Verified against Vyper v0.4.0 compiler output for CurveStableSwap pattern.