Crypto Trainingblogweb3 security engineering
<- Back to hacks

Reproduced Exploit

Zero-value transfer doubles staking rewards — AuditVault synthetic reduction

The report details a critical bug in the _claimToCredit() function of the StakedCSX.sol contract. This function has a logical error where the addition assignment operator is used instead of the plain assignment operator. This results in the credit values being doubled on each call, which can be exp…

Jan 2025•Other•logic•3 min read

Chain

Other

Category

logic

Date

Jan 2025

Source

AuditVault

PoC & write-upPoC for your local evm-hack-analyzerAuditVault PoCs

EVM Playground

Source-level debugger — step opcodes and Solidity in sync

evm-hack-analyzer

The attack is replayed in an in-browser EVM preloaded with the exact dumped fork state. The execution tree shows every call; step by Solidity line or by opcode across all depths — source, Stack, Memory, Storage, Balances (native / ERC-20 / NFT), Transient storage and Return value stay in sync. Click a tree node, opcode, or source line to jump. No backend, no live RPC.

Loading fork state…

Source & credit. Reproduction of a public audit finding curated by AuditVault — the original finding: 44004-c-01-malicious-users-can-steal-all-staking-rewards-from-stak. Standalone Foundry PoC and full write-up: 44004-c-01-malicious-users-can-steal-all-staking-rewards-from-stak_exp in the evm-hack-registry mirror.

Vulnerability classes: vuln/logic/reward-calculation · vuln/logic/state-update

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

AuditVault finding: 44004 · [C-01] Malicious Users Can Steal All Staking Rewards From StakedCSX Due to a Logical Error

Key info#

ImpactHIGH — Zero-value transfer doubles staking rewards
Protocol[[Csx]]
FindingAuditVault #44004
Reporthttps://github.com/shieldify-security/audits-portfolio-md/blob/main/CSX-Security-Review.md
SourceAuditVault finding
Compiler^0.8.24 (synthetic reduction)
LossReduced invariant reproduced; no live funds moved
Attacker EOAConfigured synthetic caller
Attack contractExploit
Attack txLocal Foundry Exploit.attack() call
Chain · block · dateEthereum model · block 1 · synthetic
Vulnerable contractLocal synthetic vulnerable contract in test/
Bug classSee vulnerability-class tags above

TL;DR#

The report details a critical bug in the _claimToCredit() function of the StakedCSX.sol contract. This function has a logical error where the addition assignment operator is used instead of the plain assignment operator. This results in the credit values being doubled on each call, which can be exploited to drain all the staking rewards from the contract. The bug has been identified in the StakedCSX.sol file and the team has recommended replacing the addition assignment operators with plain assignment operators to fix the vulnerability. The team has since removed the credit mapping and made modifications to the _updateRewardRate() function to address the issue.

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/44004-c-01-malicious-users-can-steal-all-staking-rewards-from-stak.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#

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/44004-c-01-malicious-users-can-steal-all-staking-rewards-from-stak_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/44004-c-01-malicious-users-can-steal-all-staking-rewards-from-stak.mjs.

Sources#

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

Sources & further analysis#

Reproductions & code

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.