title: Crosslinking transaction attack in hyperledger/fabric
description: 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 v2.2.14 and v2.5.5 to detect potential cross-linking issues before processing blocks. Users are advised to upgrade. There are no known workarounds for this vulnerability.
problem types: CWE-362: Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')
affected:
{
vendor: hyperledger
product: fabric
versions:
version: >= 1.0.0, < 2.2.14, status: affected
version: >= 2.3.0, < 2.5.5, status: affected
}
metrics:
cvssV3_1: [
attackComplexity: LOW
attackVector: NETWORK
availabilityImpact: LOW
baseScore: 7.1
baseSeverity: HIGH
confidentialityImpact: NONE
integrityImpact: HIGH
privilegesRequired: LOW
scope: UNCHANGED
userInteraction: NONE
vectorString: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:L
version: 3.1
]