CVE-2026-49866 in libp2p
Summary
by MITRE • 07/09/2026
libp2p is a JavaScript Implementation of libp2p networking stack. Prior to 16.0.0, @libp2p/gossipsub defaultDecodeRpcLimits set maxIhaveMessageIDs and maxIwantMessageIDs to Infinity, allowing oversized IHAVE and IWANT control message arrays in message/decodeRpc.ts and gossipsub.ts to synchronously iterate roughly 180,000 message IDs per 4 MB frame and block the Node.js event loop. This issue is fixed in version 16.0.0.
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Analysis
by VulDB Data Team • 07/09/2026
The vulnerability in libp2p's JavaScript implementation affects the @libp2p/gossipsub module prior to version 16.0.0, where default configuration parameters for message decoding contained critical design flaws that enabled denial-of-service conditions. The specific issue resides in the defaultDecodeRpcLimits configuration where maxIhaveMessageIDs and maxIwantMessageIDs were set to Infinity values within the message/decodeRpc.ts and gossipsub.ts files. This configuration allowed malicious actors to craft oversized IHAVE and IWANT control messages containing excessive numbers of message identifiers that could trigger synchronous iteration patterns within the Node.js event loop.
When these oversized control messages are processed, the system synchronously iterates through approximately 180,000 message IDs per 4 MB frame, creating substantial computational overhead that blocks the Node.js event loop for extended periods. This synchronous processing pattern directly violates the single-threaded nature of Node.js execution model, where blocking operations prevent other tasks from executing until completion. The vulnerability represents a classic example of resource exhaustion through algorithmic complexity attacks, where an attacker can cause significant performance degradation by sending relatively small control messages that trigger massive computational workloads.
The operational impact of this vulnerability extends beyond simple performance degradation to potentially enable complete service disruption in networked applications relying on libp2p gossipsub protocols. Network participants using affected versions could experience prolonged blocking periods, making the system unresponsive to legitimate traffic and effectively rendering it unavailable for normal operations. This issue particularly affects distributed systems where gossipsub protocol is used for peer-to-peer message propagation, as it can cascade through network topologies and impact multiple nodes simultaneously.
This vulnerability aligns with CWE-400 weakness classification related to Uncontrolled Resource Consumption and represents a specific instance of the broader category of denial-of-service attacks targeting event loop blocking in JavaScript environments. The ATT&CK framework categorizes this under T1499.004 for Network Denial of Service, where adversaries leverage protocol implementation flaws to exhaust system resources. The fix implemented in version 16.0.0 addresses this by establishing reasonable limits on message ID arrays, preventing the synchronous iteration of excessive values and maintaining system responsiveness.
Mitigation strategies should prioritize immediate upgrade to libp2p version 16.0.0 or later, which implements proper bounds checking for control message processing. Organizations using older versions should consider implementing additional rate limiting at network boundaries and monitoring for unusual patterns in IHAVE and IWANT message sizes. The solution demonstrates proper defensive programming principles by establishing explicit upper limits on resource consumption while maintaining protocol functionality. Security teams should also consider implementing automated detection mechanisms to identify potentially malicious control messages that exceed normal operational parameters, particularly in environments where untrusted peers may participate in the gossipsub network topology.