Unlocking percentage formula applies an 80% penalty — AuditVault synthetic reduction

Source & credit. Reproduction of a public audit finding curated by AuditVault — the original finding: 43732-h-1-fluidlocker-getunlockingpercentage-incorrectly-divides-o. Standalone Foundry PoC and full write-up: 43732-h-1-fluidlocker-getunlockingpercentage-incorrectly-divides-o_exp in the evm-hack-registry mirror.

Vulnerability classes: vuln/arithmetic/precision-loss · vuln/logic/price-calculation

Reproduction: self-contained Foundry PoC with an offline synthetic contract. Full trace: output.txt.

AuditVault finding: 43732 · H-1: FluidLocker::_getUnlockingPercentage()incorrectly divides one of the components of the formula byS, leading to always having 80% penalty

Key info#


Impact	HIGH — Unlocking percentage formula applies an 80% penalty
Protocol	[[Superfluid]] Locking Contract
Finding	AuditVault #43732
Report	https://github.com/sherlock-audit/2024-11-superfluid-locking-contract-judging
Source	AuditVault finding
Compiler	`^0.8.24` (synthetic reduction)
Loss	Reduced invariant reproduced; no live funds moved
Attacker EOA	Configured synthetic caller
Attack contract	`Exploit`
Attack tx	Local Foundry `Exploit.attack()` call
Chain · block · date	Ethereum model · block 1 · synthetic
Vulnerable contract	Local synthetic vulnerable contract in `test/`
Bug class	See vulnerability-class tags above

TL;DR#

The bug report discusses an issue with the FluidLocker::_getUnlockingPercentage() function in the Superfluid locking contract. The function incorrectly divides one of the components of the formula by S, resulting in a 80% penalty for users unlocking their Fluid. This bug was found by a group of security researchers and the root cause was identified in line 388 of the code. The bug can be exploited by a user unlocking their Fluid with a duration greater than 0, causing them to suffer a significant loss. A proof of concept was provided and the fix for this issue has been included in a pull request by the protocol team.

Background#

The upstream report is a Solidity finding. This page keeps the vulnerable statement and demonstrates its security consequence in a small, deterministic EVM model; no live RPC or external dependencies are required.

The vulnerable code#

SOLIDITY

// The exact vulnerable pattern is retained in test/43732-h-1-fluidlocker-getunlockingpercentage-incorrectly-divides-o.sol.
// @> see the marked statement in the synthetic reduction

Root cause#

The caller-controlled input or stale state is trusted before the required uniqueness, bounds, authorization, accounting, or reentrancy invariant is enforced. The marked line in the synthetic contract intentionally preserves that ordering so the assertion is executable.

Preconditions#

The vulnerable contract is deployed with the state described by the report.
The attacker can reach the affected entry point (or submit the report's crafted input).

Attack walkthrough#

Exploit.run() initializes the minimal state from the report.
The marked vulnerable operation executes without its required check.
The contract records the resulting invariant violation and emits a Proof event.
The test asserts the harm; the passing trace is recorded at output.txt:4.

Diagrams#

flowchart TD A[Attacker supplies crafted input] --> B[Vulnerable operation] B --> C{Missing invariant check} C --> D[Security impact demonstrated]

sequenceDiagram participant A as Attacker participant V as Vulnerable contract participant S as State A->>V: invoke affected entry point V->>S: apply unchecked update S-->>A: harm is observable

Remediation#

Apply the invariant before mutating state: accrue interest before adding principal; reject duplicate signers; use checked casts and bounded lengths; validate token/target/DAO identities; use nonReentrant; enforce slippage and fee equality; and validate the canonical authority or ownership relationship described by the report.

How to reproduce#

BASH

cd evm-hack-registry/43732-h-1-fluidlocker-getunlockingpercentage-incorrectly-divides-o_exp
forge test -vvvvv

The test is offline and uses only the shared forge-std library. The corresponding Playground bundle is generated from scripts/poc-configs/43732-h-1-fluidlocker-getunlockingpercentage-incorrectly-divides-o.mjs.

Sources#

Reference: https://github.com/sherlock-audit/2024-11-superfluid-locking-contract-judging

Sources & further analysis#

Reproductions & code

Standalone PoC + full trace: 43732-h-1-fluidlocker-getunlockingpercentage-incorrectly-divides-o_exp (evm-hack-registry mirror).
AuditVault finding: 43732-h-1-fluidlocker-getunlockingpercentage-incorrectly-divides-o.

Alerts & third-party analyses

Web3Sec X hacked database: search.
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Solodit incident search: search.

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