Project

Summary

The contract utilizes abi.encodePacked() with user-controlled byte arrays, which can potentially lead to hash collisions. This occurs because abi.encodePacked() concatenates values without distinguishing the boundaries of byte arrays, allowing attackers to manipulate input data to produce the same hash for different inputs. This vulnerability could be exploited to interfere with the contract's integrity, potentially allowing attackers to bypass access control checks, manipulate signatures, or cause unexpected behavior in critical operations.

Vulnerability Details

The function abi.encodePacked() is commonly used to concatenate data, and in this contract, it is employed to generate hashes for certain operations. However, abi.encodePacked() does not provide length prefixes for variable-length types like bytes, which can cause collisions if user-controlled byte arrays are involved. An attacker can craft two different byte arrays that result in the same output when concatenated and hashed, leading to unintended consequences like the misidentification of function selectors or parameters.

The userAddress is a dynamic-length byte array. An attacker could control or influence the contents of userAddress and craft a different array that, when concatenated with functionSignature, results in the same hash. This would allow the attacker to bypass certain logic, such as function selectors or authorization checks, leading to security breaches.

Link of the Affected Code

• https://github.com/Cyfrin/2024-11-one-world/blob/1e872c7ab393c380010a507398d4b4caca1ae32b/contracts/meta-transaction/NativeMetaTransaction.sol#L63

Impact

This vulnerability can lead to hash collisions due to the improper use of abi.encodePacked(), a function that concatenates variables into a single byte array for hashing. Hash collisions can create unexpected behaviors, such as misidentification of unique values or incorrect contract logic execution, which can be exploited by attackers to bypass security checks or cause incorrect contract behavior.

The likelihood of this vulnerability being exploited depends on how widely the affected function is used, how the contract handles critical operations, and how much control the attacker has over the userAddress or other byte arrays passed into abi.encodePacked(). If the contract allows external actors to control any part of the byte array (such as userAddress), the likelihood of this vulnerability being exploited increases. Given that Ethereum contracts often rely on secure hash-based mechanisms for signature verification, authentication, and other critical operations, the exploitation of this vulnerability could be relatively easy if attackers can manipulate the input.

The most harmful consequence of this vulnerability is the possibility of hash collisions that could interfere with key operations within the smart contract. If an attacker can generate a collision between two different byte arrays (such as two different addresses or function signatures), they could trick the contract into thinking the data has a different meaning. This could lead to:

1. Bypassing Security Checks: If the contract uses hashes for validation, such as for signature verification or authorization checks, hash collisions could allow an attacker to gain unauthorized access.

2. Incorrect Contract Behavior: A hash collision could cause the contract to misidentify function calls, leading to incorrect state changes or execution of unintended logic.

3. Signature Manipulation: If the contract relies on hashed data for signature validation (e.g., meta-transactions), attackers may be able to craft a fake valid signature using a collision, allowing them to perform unauthorized actions.

4. Potential for Exploitation: Exploiting this vulnerability, an attacker could execute arbitrary functions or manipulate critical contract behavior, leading to financial losses, theft, or malicious exploitation.

Proof of Concept

An attacker could craft two different byte arrays that would result in the same hash when passed to abi.encodePacked().

For example, suppose:

• functionSignature = 0xabcdef... (some fixed byte array representing the function signature)

• userAddress = 0x1234... (some byte array representing a user address)
  An attacker might be able to find a different byte array userAddress2 such that:

This results in a hash collision, allowing the attacker to bypass security checks that depend on unique hashes.

Tools Used

Manual Review

Recommendations

To prevent hash collisions, it is recommended to use abi.encode() instead of abi.encodePacked(). Unlike abi.encodePacked(), abi.encode() adds length prefixes to the variables it encodes, which helps distinguish between different byte arrays and prevents potential collisions. Additionally, it is important to avoid passing user-controlled byte arrays directly into abi.encodePacked() to reduce the attack surface for potential collision-based exploits.

This approach ensures that byte arrays are encoded with proper length prefixes, preventing hash collisions and maintaining the integrity of the data being processed.