USDT claim underflows when contract has a larger balance — AuditVault synthetic reduction

Source & credit. Reproduction of a public audit finding curated by AuditVault — the original finding: 44006-h-02-the-usdt-reward-claiming-functionality-of-vestedstaking. Standalone Foundry PoC and full write-up: 44006-h-02-the-usdt-reward-claiming-functionality-of-vestedstaking_exp in the evm-hack-registry mirror.

Vulnerability classes: vuln/arithmetic/underflow · vuln/dos/frozen-funds

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

AuditVault finding: 44006 · [H-02] The USDTReward Claiming Functionality ofVestedStaking Can Be DoSed Due to a Logical Error

Key info#

TL;DR#

This bug report describes a high-risk issue in the claimRewards function of the VestedStaking.sol contract. The issue affects the calculation of USDT rewards and can be exploited by malicious users to prevent others from claiming their rewards. A proof of concept test is included to demonstrate the issue. The affected code is located on line 170 of the VestedStaking.sol file. The recommended solution is to fetch the balance of the msg.sender instead of the current contract. The team has responded that the issue has been fixed as suggested.

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#

// The exact vulnerable pattern is retained in test/44006-h-02-the-usdt-reward-claiming-functionality-of-vestedstaking.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#

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

Diagrams#

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#

cd evm-hack-registry/44006-h-02-the-usdt-reward-claiming-functionality-of-vestedstaking_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/44006-h-02-the-usdt-reward-claiming-functionality-of-vestedstaking.mjs.

Sources#

• AuditVault finding
• https://github.com/shieldify-security/audits-portfolio-md/blob/main/CSX-Security-Review.md
• Synthetic test

Reference: https://github.com/shieldify-security/audits-portfolio-md/blob/main/CSX-Security-Review.md

Sources & further analysis#

Reproductions & code

• Standalone PoC + full trace: 44006-h-02-the-usdt-reward-claiming-functionality-of-vestedstaking_exp (evm-hack-registry mirror).
• AuditVault finding: 44006-h-02-the-usdt-reward-claiming-functionality-of-vestedstaking.

Alerts & third-party analyses

• Web3Sec X hacked database: search.
• Rekt leaderboard: search.
• Solodit incident search: search.

These dashboards index community alerts tweets, post-mortems, and independent write-ups. Reach them through the protocol name above to cross-check this reproduction against other analyses.