Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')

Summary

Hyperledger Fabric is an open-source permissioned distributed ledger framework. Combining two molecules to one another, called "cross-linking" results in a molecule with a chemical formula that is composed of all atoms of the original two molecules. In Fabric, one can take a block of transactions and cross-link the transactions in a way that alters the way the peers parse the transactions. If a first peer receives a block B and a second peer receives a block identical to B but with the transactions being cross-linked, the second peer will parse transactions in a different way and thus its world state will deviate from the first peer. Orderers or peers cannot detect that a block has its transactions cross-linked because there is a vulnerability in the way Fabric hashes the transactions of blocks. It simply and naively concatenates them, which is insecure, and lets an adversary craft a "cross-linked block" (block with cross-linked transactions) which alters the way peers process transactions. For example, it is possible to select a transaction and manipulate a peer to completely avoid processing it, without changing the computed hash of the block. Additional validations have been added in versions 1.0.0-alpha through 2.2.13, 2.3.0 through 2.5.4, and 3.0.0-preview to detect potential cross-linking issues before processing blocks. Users are advised to upgrade. There are no known workarounds for this vulnerability.