Roast Football Lost Funds through Exploited Reward System

TL;DR#

On December 05, 2022, Roast Football was a victim of an attack, in which the exploiter repeatedly swapped $RBF and $WBNB tokens by manipulating their reward system to book a profit of approximately 12 $BNB worth $3500.

The occurrence of this exploit is unique when compared to the other analyses that we have covered. The project's smart contract operation also relied on the block number and time stamp, which was eventually exploited by the attacker.

Introduction to Roast Football#

Roast Football $RBF is a BSC token, which according to the team, follows the roast beef model for the world's first soccer hot spot, as well as the lottery mechanism double economic model.

Vulnerability Assessment#

The vulnerability is caused by a weak pseudorandom number generator in the lottery function, which executes transactions only when the lottery is won.

Steps#

• We tried to analyse the attack transaction, executed by the exploiter.
• The Roast Football contract includes a randMod function that uses the parameters buyer and buyAmount to generate a random number. This random number is then used to determine whether the withdrawDistributor or withdrawPlazz functions on the distributor contract should be called.

• They have a lottery mechanism that gives users a chance of receiving a 10x reward when they purchase the $RFB.
• This perpetrator only purchased $RFB tokens when he was certain he would win the lottery.
• If the exploiter does not win the lottery, the function will revert, and losing in the gas fees.
• The exploiter was funded by Tornado Cash, and his lottery profits for winning two out of fifty times are still available at his address.

Aftermath#

The team has not released a post-mortem report detailing the incident.

How to prevent such an attack vector#

There are many a potential issues with the implementation of this function. The use of block number, and time stamp in the generation of a random number can be exploited by an attacker who can predict these values. This would allow an attacker to manipulate the outcome of the random number generation, and gain an unfair advantage in the distribution of the funds.

The use of catch statement to ignore any errors in the transfer of funds may also hide potential issues with the transfer of funds.

The impact of this attack could have been significantly reduced if Roast Football had a dedicated cover pool in the Neptune Mutual marketplace. We have standard terms and conditions in place to provide coverage to various types of DeFi attacks, but we are also open to make exceptions in some cases.

Users who purchase our parametric cover policies do not need to provide loss evidence in order to receive payouts. Payouts can be claimed as soon as an incident like this is resolved through our governance system.

Additionally, auditing the smart contracts for vulnerabilities is insufficient due to the existence of varying attack vectors. Neptune Mutual's security team can also assess your preferred protocol for DNS and web-based security, smart contract evaluations, and frontend and backend security.

Reference Source
CertiK, BlockSec