Cyber Incident Victim: ZenCash
Date:
Jun 2018
Location:
United States of America
Summary
The ZenCash network experienced a 51% attack resulting in two successful double-spend transactions totaling approximately $550,000 worth of ZEN. The attacker reorganized 38 blocks, exploiting vulnerabilities inherent to its Equihash-based proof-of-work consensus mechanism. Network developers responded by increasing confirmation time requirements to 100 blocks and collaborating with exchanges to mitigate further risks. Forensic analysis identified a suspect mining pool address and an associated exchange deposit address involved in the attack. The incident highlighted exposure to hash power manipulation, as the network's 58MSol/s hashrate was overwhelmed by the attacker's private mining operation and potential rented computational resources.
| CIA Posture | Motives | Tactics, Techniques & Procedures |
|---|---|---|
| Available to members | 1 motive | 1 technique |
| Threat Actors | Type | Location |
|---|---|---|
| 0 actors | Available to members | Available to members |
Description
On June 2, 2018, the ZenCash network experienced a 51% attack that resulted in two successful double-spend transactions. The attacker executed blockchain reorganizations between blocks 318165 and 318275, reverting 38 blocks during the longest reorganization. The double-spend attacks occurred specifically in blocks 318204 and 318234, involving 13,000 ZEN and 6,600 ZEN respectively, equivalent to over $550,000 at prevailing exchange rates. Prior to the attack, ZenCash developers received warnings from a pool operator about potential vulnerabilities, prompting initial defensive preparations. During the incident, the network's hashrate stood at 58MSol/s, with forensic analysis identifying the suspect pool address as znkMXdwwxvPp9jNoSjukAbBHjCShQ8ZaLib and the exchange deposit address as zneDDN3aNebJUnAJ9DoQFys7ZuCKBNRQ115. Investigators concluded the attacker likely utilized a combination of private mining infrastructure and rented hash power to overwhelm the Equihash-based proof-of-work network, which was inherently vulnerable to sudden influxes of external mining capacity.
Following the attack, ZenCash developers implemented immediate countermeasures focused on increasing network security. They contacted cryptocurrency exchanges to recommend extending confirmation times to a minimum of 100 blocks for ZenCash transactions, significantly raising the computational cost required for future double-spend attempts. The team publicly disclosed technical details of the attack vectors to facilitate industry-wide awareness about Equihash vulnerabilities. Forensic examination revealed the attacker exploited ZenCash's susceptibility to hashpower manipulation, though no specific perpetrator identification or law enforcement actions were detailed in available reports. The incident highlighted systemic risks for smaller proof-of-work cryptocurrencies facing concentrated mining resources, with ZenCash's market value and operational stability directly impacted by the substantial financial losses and blockchain integrity breach. No subsequent attacks were reported following these defensive adjustments during the documented observation period.