OpenVM byte decomposition of pc in AUIPC chip can overflow

Vulnerability Description

OpenVM is a performant and modular zkVM framework built for customization and extensibility. In version 1.0.0, OpenVM is vulnerable to overflow through byte decomposition of pc in AUIPC chip. A typo results in the highest limb of pc being range checked to 8-bits instead of 6-bits. This results in the if statement never being triggered because the enumeration gives i=0,1,2, when instead the enumeration should give i=1,2,3, leaving pc_limbs[3] range checked to 8-bits instead of 6-bits. This leads to a vulnerability where the pc_limbs decomposition differs from the true pc, which means a malicious prover can make the destination register take a different value than the AUIPC instruction dictates, by making the decomposition overflow the BabyBear field. This issue has been patched in version 1.1.0.

References

• https://github.com/openvm-org/openvm/security/advisories/GHSA-jf2r-x3j4-23m7
• https://github.com/openvm-org/openvm/commit/68da4b50c033da5603517064aa0a08e1bbf70a01
• https://cantina.xyz/code/c486d600-bed0-4fc6-aed1-de759fd29fa2/findings/21
• https://github.com/openvm-org/openvm/blob/0f94c8a3dfa7536c1231465d1bdee5fc607a5993/extensions/rv32im/circuit/src/auipc/core.rs#L135
• https://github.com/openvm-org/openvm/releases/tag/v1.1.0