CVE-2013-2293 in bitcoind
Summary
by MITRE
The CTransaction::FetchInputs method in bitcoind and Bitcoin-Qt before 0.8.0rc1 copies transactions from disk to memory without incrementally checking for spent prevouts, which allows remote attackers to cause a denial of service (disk I/O consumption) via a Bitcoin transaction with many inputs corresponding to many different parts of the stored block chain.
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Analysis
by VulDB Data Team • 02/25/2019
The vulnerability described in CVE-2013-2293 represents a critical denial of service weakness in the Bitcoin protocol implementation prior to version 0.8.0rc1. This flaw exists within the core transaction processing logic of bitcoind and Bitcoin-Qt clients, specifically in how they handle transaction input validation during the FetchInputs method execution. The vulnerability stems from a fundamental design oversight that fails to implement proper validation of previous transaction outputs during the loading process from persistent storage. When a malicious actor crafts a specially constructed transaction containing an excessive number of inputs, each referencing distinct locations within the blockchain history, the affected software begins an inefficient process of loading and verifying these inputs from disk storage.
The technical implementation of this vulnerability manifests through the absence of incremental validation mechanisms that should occur during the transaction input fetching process. Rather than validating each previous output reference as it is loaded from disk, the vulnerable code performs a bulk loading operation that retrieves all referenced transactions without checking whether their outputs have already been spent. This approach creates a scenario where a single malicious transaction can trigger the system to access numerous disparate sections of the blockchain database, leading to excessive disk I/O operations and resource consumption. The flaw operates at the level of the transaction validation subsystem, which is a core component of the Bitcoin node's integrity verification process, making it particularly dangerous as it can be exploited by any network participant without requiring special privileges or access rights.
The operational impact of this vulnerability extends beyond simple resource exhaustion, as it can effectively render Bitcoin nodes unusable for extended periods. Attackers can construct transactions with hundreds or thousands of inputs, each pointing to different parts of the blockchain history, forcing the affected software to perform an exponential number of disk reads. This creates a cascading effect where the node's performance degrades significantly, potentially leading to complete service unavailability. The vulnerability is particularly concerning because it can be exploited through legitimate network traffic without requiring any special authentication or authorization, making it a prime candidate for distributed denial of service attacks against Bitcoin infrastructure. Network participants may experience complete system lockups, slow transaction processing, or complete failure to process new transactions while the malicious inputs are being validated. The impact is further amplified by the fact that Bitcoin nodes typically store complete blockchain history, meaning that the disk I/O operations can involve accessing thousands of different database entries scattered throughout the storage system.
Mitigation strategies for this vulnerability require both immediate code-level fixes and architectural improvements to prevent similar issues in the future. The primary solution involves implementing incremental validation of previous outputs during the transaction input fetching process, ensuring that each referenced transaction output is checked for spending status before proceeding with the loading operation. This approach aligns with security best practices for database access patterns and prevents the exponential growth in I/O operations that characterizes this attack vector. The fix should include proper caching mechanisms to avoid redundant database lookups and implement reasonable limits on the number of inputs that can be processed in a single transaction. Additionally, the implementation should follow established security frameworks such as those outlined in the CWE (Common Weakness Enumeration) catalog, specifically addressing weakness categories related to resource management and input validation. Organizations should also consider implementing network-level controls to monitor for anomalous transaction patterns and establish rate limiting mechanisms to prevent exploitation. The vulnerability highlights the importance of proper defensive programming practices and the necessity of implementing comprehensive input validation at multiple layers of the system architecture, as recommended by ATT&CK framework methodologies for preventing resource exhaustion attacks.