A newly disclosed transaction-relay jamming vulnerability has raised concerns about the security of Bitcoin nodes, particularly in the context of time-sensitive contracting protocols like the Lightning Network.
This attack exploits the transaction selection, announcement, and propagation mechanisms of Bitcoin’s base-layer full nodes, potentially enabling attackers to disrupt transactions and steal funds from Lightning channels.
Transaction-Relay Jamming Vulnerability
The vulnerability involves two variations of a “transaction-relay throughput attack”: the “high overflow” and “low overflow” variants. These attacks target specific limits in Bitcoin’s transaction-relay system:
- High Overflow Attack: This variant manipulates the fee-rate sorting mechanism and inventory broadcast limits of a node’s transaction inventory. By flooding a node with high-fee, low-value transactions, an attacker can prevent lower-fee, time-sensitive transactions (such as those used in Lightning channels) from propagating through the network. This disruption can lead to financial losses for victims.
- Low Overflow Attack: This variant exploits the maximum number of transaction announcements a node can process from its peers. By overwhelming a node with excessive transaction announcements, attackers can force legitimate transactions to be dropped or delayed.
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Both attacks exploit inherent throughput limitations in Bitcoin’s peer-to-peer network, making them particularly concerning for systems relying on timely transaction propagation.
According to the report shared by Ariard in Github, the Lightning Network, which relies on pre-signed, time-sensitive transactions to secure off-chain payments, is especially vulnerable to these attacks.
For instance, in the high overflow attack scenario, an attacker could prevent a victim’s justice or timeout transactions from propagating before their timelocks expire. This could allow an attacker to claim funds unfairly or cause financial loss to channel participants.
Several mitigation strategies have been proposed to counter these attacks:
- Random Transaction Rebroadcasting: Periodically rebroadcasting time-sensitive transactions may reduce the likelihood of them being blocked.
- Dynamic Fee Adjustment: Increasing fees for critical transactions could help them bypass jamming attempts but may expose users to miner exploitation.
- Over-Provisioning Nodes: Deploying additional full nodes connected to trusted peers could absorb excess traffic and ensure transaction propagation.
- Limiting Identical Finality Transactions: Restricting the number of simultaneous time-sensitive transactions could reduce network congestion.
While these measures provide some protection, experts agree that addressing the issue at Bitcoin’s base layer would offer more robust and long-term solutions.
The vulnerability was initially reported to prominent Bitcoin and Lightning developers in mid-2023. After months of discussions and testing, it was publicly disclosed in December 2024. The attack is currently being tracked under CVE Request 1780258 by MITRE.
This new transaction-relay jamming vulnerability highlights critical weaknesses in Bitcoin’s transaction-relay mechanisms that can be exploited against off-chain protocols like the Lightning Network.
While no real-world exploits have been observed yet, further research and mitigation efforts are essential to safeguard users against these sophisticated attacks.
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