Security and Privacy in Permissioned Blockchain Interoperability: A Systematic Review

Blockchain interoperability enables seamless communication and asset transfer across isolated permissioned blockchain systems, but it introduces significant security and privacy vulnerabilities. This review aims to systematically assess the security and privacy landscape of interoperability protocols for permissioned blockchains, identifying key properties, attack vectors, and countermeasures. Using PRISMA 2020 guidelines, we analysed 56 peer-reviewed studies published between 2020 and 2025, retrieved from Scopus, ScienceDirect, Web of Science, and IEEE Xplore. The review focused on interoperability protocols for permissioned blockchains with security and privacy analyses, including only English-language journal articles and conference proceedings. Risk of bias in the included studies was assessed using the MMAT. Methods for presenting and synthesizing results included descriptive analysis, bibliometric analysis, and content analysis, with findings organized into tables, charts, and comparative summaries. The review classifies interoperability protocols into relay, sidechain, notary scheme, HTLC, and hybrid types and identifies 18 security and privacy properties along with 31 known attack types. Relay-based protocols showed the broadest security coverage, while HTLC and notary schemes demonstrated significant security gaps. Notably, 93% of studies examined fewer than four properties or attack types, indicating a fragmented research landscape. The review identifies underexplored areas such as ACID properties, decentralization, and cross-chain attack resilience. It further highlights effective countermeasures, including cryptographic techniques, trusted execution environments, zero-knowledge proofs, and decentralized identity schemes. The findings suggest that despite growing adoption, current interoperability protocols lack comprehensive security evaluations. More holistic research is needed to ensure the resilience, trustworthiness, and scalability of cross-chain operations in permissioned blockchain ecosystems.