OpenZeppelin Confidential Contracts `VestingWalletConfidential`: a malicious ERC-7984 token is able to extract private data from the vesting wallet

Impact

Two locations consume an encrypted handle returned by an untrusted external party and use it without verifying that the party is ACL-authorized on it.

VestingWalletConfidential

Malicious users can call release with a malicious token. This token could return an alternative handle on confidentialBalanceOf, which represents the balance of the vesting wallet on an alternative ERC-7984 token (or any other handle that the vesting wallet has access to). The vesting wallet does not check that the token has ACL access and grants access to a new handle derived from the returned handle.

Effectively, this bug allows a malicious user to gain information about any private euint64 handle that the vesting wallet has access to via a malicious ERC-7984 token. There is no loss of funds.

ERC7984

On a transfer with callback, ERC7984 uses the ebool returned by the recipient's IERC7984Receiver.onConfidentialTransferReceived to drive the refund logic, without checking that the recipient has ACL access to it. A malicious recipient can return any ebool the token has access to and recover its plaintext from the refund result, which the token grants the caller access to. The leak is limited to ebool handles (the value is only used as an FHE.select condition), and there is no loss of funds.

Patches

Both issues were fixed in the same patch releases: v0.5.2, v0.4.2, v0.3.2

• VestingWalletConfidential: 93e75ceed2b9648f53f9d133f431064353456805 (#423).
• ERC7984 transfer callback: fe0863af2c9dce7614acce98720a913bf6a767a5 (#428), with follow-up ee47edf189ab681cebdad18bfb53dee541987be2 (#431) permitting an uninitialized returned handle.