CVE-2026-62333: OpenVM: MemoryMerkleAir allows below-leaf rows to alter memory roots

OpenVM is a performant and modular zkVM framework built for customization and extensibility. Before 1.7.0 in the 1.x line and in affected 2.0 and 2.1 prereleases, MemoryMerkleAir does not forbid Merkle expansion rows at parentheight = 0 or below while expanddirection != 0. A malicious prover can fabricate a subtree below a memory leaf and swap digests inside that subtree to change the committed memory root without a corresponding memory operation. The fraudulent rows still balance against the Merkle and compression buses and require no memory-bus operation for the changed leaf. Because the memory Merkle root binds VM memory state across continuation segment boundaries, this affects the soundness of OpenVM proofs using persistent memory. This issue is fixed in versions 1.7.0, 2.0.0-rc.3 and 2.1.0-preview.