# The Blockchain Oracle Problem in Decentralized Finance--A Multivocal Approach
## 5 Risks and Attack Vectors
### Sybil Attacks (S)  
Sybil attacks are means to manipulate decentralized oracle platforms. To obtain the majority of votes, the Sybil replicates its vote to gain a higher weight when compared to others [14]. Equally, the Sybil can also manipulate other oracles for them to display the same choice as its own. Sybil schemes are only possible in systems where the oracle identity is anonymous, and their choice is private. In an interesting paper, Douceur [106] explains that the only way to prevent a Sybil attack is to make the voters' identity public and their choices transparent. In decentralized systems, influencing the majority of voters can also be identified as a 51% attack. Unlike those that can be performed on a Proof-of-work protocol, it does not involve computing power but refers to the corruption of enough voters to be able to control the outcome of an oracle feed. Alternatively, it may refer to a condition in which agents with enough voting power collude to change the rules for selfish purposes. On MakerDAO, for example, due to the fact that a restricted number of Maker holders take decisions on oracles, Liu et al. [17], hypothesized that a 51% attack was then possible and expectable. Basically, due to the concentration of Maker owners and their low participation in the voting process, collusion to manipulate governance and price oracles is perceived, extremely likely. The thesis was also supported by other studies [107; 108; 109],  
Figure 7: Example of a front-running opportunity.  
which confirms the chances of performing governance attacks on MakerDAO, as well as other DeFi platforms, eventually pushing the entire DeFi ecosystem to a crisis. However, the thesis is confirmed mainly by the fact that, on October 2020, an attacker used a flash loan to borrow enough MKR to pass a governance proposal to change the MKR oracle whitelist parameter and managed to push his feeder to the allowlist [63; 110]. Therefore, Sybil attacks cannot be underestimated. Those attacks can also be performed through mirroring and freeloading.  
_Mirroring:_ In mirroring attacks, the Sybil honestly works for the platform executing the data collection as requested. However, to guarantee the data collection's major weight, it \"mirrors\" the data collected into different oracles under its control. That technique ensures the lowest cost of data collection and the highest chance of selling the data to the customer platform. Again, in an anonymity and privacy condition, the chance of spotting a mirroring attack is quite low [6].  
_Freeloading:_ Extensively explained in the Augur whitepaper [33], the freeloading attack is a technique thanks to which an oracle replicates the data fetched by another entity, without making the effort of performing the data collection itself. Since the data are obtained effortlessly, the Sybil can provide the service at a lower price than the honest oracles, eventually pushing them out of the market. Once the honest oracles are out of play, the system is solely managed by malevolent or corrupt oracles [20]. In off-chain acquisition, this vulnerability can easily be overcome using a Commit/Reveal design pattern (e.g., Razor Network), which ensures that cleartext data is only revealed when the transaction is ready to be finalized. This pattern also provides a guarantee that the data eventually revealed cannot be changed. If the results are always transparent, then it is harder to counter. Although possible, this type of attack is quite rare, and, as explained in the Augur whitepaper, it never constituted a real threat.