TraitForge generation rollover is permanently blocked by the wrong modifier

Source & credit. Reproduction of a public audit finding curated by AuditVault — the original finding: 37920-h-06-minttoken-mintwithbudget-and-forge-in-the-traitforgenft. Standalone Foundry PoC and full write-up: 37920-h-06-entropy-generator-initialize-alpha-indices-wrong-modifier-code4rena_exp in the evm-hack-registry mirror.

Vulnerability classes: vuln/access-control/missing-modifier · vuln/dos/init-constraint · vuln/logic/wrong-condition Reproduction: local synthetic Foundry test; output.txt and test source.

Key info#

TL;DR#

TraitForgeNft is configured as EntropyGenerator.allowedCaller, but the audited function uses onlyOwner. On every generation rollover the NFT calls initializeAlphaIndices; msg.sender is the NFT, not the owner, so the call reverts. The first capped mint in this reduction is therefore uncallable.

The vulnerable code#

The finding quotes the exact declaration:

function initializeAlphaIndices() public whenNotPaused onlyOwner { // @> VULN
    // initialize alpha indices
}

The fix is the one-line modifier change:

- function initializeAlphaIndices() public whenNotPaused onlyOwner {
+ function initializeAlphaIndices() public whenNotPaused onlyAllowedCaller {

Root cause and preconditions#

The contract has two distinct authorities: the deployment owner and the NFT contract allowed to update alpha indices. The function protects the latter operation with the former role. No unusual setup is needed; ordinary traffic that reaches the generation cap activates the broken call.

Attack walkthrough#

1. Exploit deploys EntropyGenerator, then TraitForgeNft, and configures the NFT as allowedCaller.
2. mintToken() reaches the one-token generation cap and calls _incrementGeneration().
3. _incrementGeneration() calls initializeAlphaIndices() from the NFT address. onlyOwner rejects that caller and the complete mint reverts.
4. Exploit.run() catches the revert and asserts total supply, generation, and alpha-index version remain unchanged. The owner-only control call succeeds, isolating the bug to the modifier.

Diagrams#

Impact and remediation#

The protocol's minting and forging flows can be permanently unavailable at each generation boundary. Replace onlyOwner with onlyAllowedCaller on initializeAlphaIndices, then retain owner-only protection for administrative functions such as setting the allowed caller.

How to reproduce#

cd 37920-h-06-entropy-generator-initialize-alpha-indices-wrong-modifier-code4rena_exp
forge test -vvvvv

This is a local synthetic with no RPC, fork, or fabricated token profit.

Sources#

• AuditVault finding #37920
• Code4rena TraitForge report
• EntropyGenerator.sol at audited commit
• TraitForgeNft.sol rollover call

Reference: Code4rena TraitForge 2024-07, finding #37920.

Sources & further analysis#

Reproductions & code

• Standalone PoC + full trace: 37920-h-06-entropy-generator-initialize-alpha-indices-wrong-modifier-code4rena_exp (evm-hack-registry mirror).
• AuditVault finding: 37920-h-06-minttoken-mintwithbudget-and-forge-in-the-traitforgenft.

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.