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.
The product contains a code sequence that can run concurrently with other code, and the code sequence requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence that is operating concurrently.
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Fabric | Hyperledger | 1.0.0 (including) | 2.2.14 (excluding) |
| Fabric | Hyperledger | 2.3.0 (including) | 2.5.5 (excluding) |
This can have security implications when the expected synchronization is in security-critical code, such as recording whether a user is authenticated or modifying important state information that should not be influenced by an outsider. A race condition occurs within concurrent environments, and is effectively a property of a code sequence. Depending on the context, a code sequence may be in the form of a function call, a small number of instructions, a series of program invocations, etc. A race condition violates these properties, which are closely related:
A race condition exists when an “interfering code sequence” can still access the shared resource, violating exclusivity. Programmers may assume that certain code sequences execute too quickly to be affected by an interfering code sequence; when they are not, this violates atomicity. For example, the single “x++” statement may appear atomic at the code layer, but it is actually non-atomic at the instruction layer, since it involves a read (the original value of x), followed by a computation (x+1), followed by a write (save the result to x). The interfering code sequence could be “trusted” or “untrusted.” A trusted interfering code sequence occurs within the product; it cannot be modified by the attacker, and it can only be invoked indirectly. An untrusted interfering code sequence can be authored directly by the attacker, and typically it is external to the vulnerable product.