CVE-2025-52884

RISC Zero is a zero-knowledge verifiable general computing platform, with Ethereum integration. The risc0-ethereum repository contains Solidity verifier contracts, Steel EVM view call library, and supporting code. Prior to versions 2.1.1 and 2.2.0, the Steel.validateCommitment Solidity library function will return true for a crafted commitment with a digest value of zero. This violates the semantics of validateCommitment, as this does not commitment to a block that is in the current chain. Because the digest is zero, it does not correspond to any block and there exist no known openings. As a result, this commitment will never be produced by a correct zkVM guest using Steel and leveraging this bug to compromise the soundness of a program using Steel would require a separate bug or misuse of the Steel library, which is expected to be used to validate the root of state opening proofs. A fix has been released as part of risc0-ethereum 2.1.1 and 2.2.0. Users for the Steel Solidity library versions 2.1.0 or earlier should ensure they are using Steel.validateCommitment in tandem with zkVM proof verification of a Steel program, as shown in the ERC-20 counter example, and documentation. This is the correct usage of Steel, and users following this pattern are not at risk, and do not need to take action. Users not verifying a zkVM proof of a Steel program should update their application to do so, as this is incorrect usage of Steel.

Weakness

The product does not properly filter, remove, quote, or otherwise manage the invalid use of special elements in user-controlled input, which could cause adverse effect on its behavior and integrity.

Potential Mitigations

• Assume all input is malicious. Use an “accept known good” input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does.
• When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, “boat” may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as “red” or “blue.”
• Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code’s environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.

References

• https://docs.beboundless.xyz/developers/steel/how-it-works#verifying-the-proof-onchain
• https://github.com/risc0/risc0-ethereum/blob/ff0cb9253a87945b653b825711b8b5075f8b7545/examples/erc20-counter/contracts/src/Counter.sol#L56-L63
• https://github.com/risc0/risc0-ethereum/commit/3bbac859c7132b21ba5fdf2d47f1dd52e7e73d98
• https://github.com/risc0/risc0-ethereum/pull/605
• https://github.com/risc0/risc0-ethereum/releases/tag/v2.1.1
• https://github.com/risc0/risc0-ethereum/releases/tag/v2.2.0
• https://github.com/risc0/risc0-ethereum/security/advisories/GHSA-gjv3-89hh-9xq2