Developer James Hilliard, best known for his Bitcoin Improvement Proposal number 91 and the CGMiner program, discovered a vulnerability in Bitmain’s Antminer S15 firmware.
Hilliard said Twitter user 00whiterabbit wrote an attack code testing the vulnerability. They wanted to show how dangerous the attack might be—the exploit allowed them to do whatever they wanted. They could modify the payout address, shut down the mining altogether, or replace the firmware. While an attack like that would be rendered difficult by a firewall, the possibility of the exploit remains.
When exploited, the vulnerability gives users root access to the machine — which is supposed to be impossible. In theory, this can be done remotely using just the IP address of the miner, and means the machine can be reprogrammed to do just about anything. This includes mining to a different Bitcoin address or having it stop mining entirely. The firmware could also be replaced by different firmware altogether (such as Braiins OS or Dragonmint firmware).
Security vulnerabilities are one of the main arguments in favor of open source software. There is no code that doesn’t benefit from the public review of the very people who might otherwise attack it. Especially when users have an incentive to turn over findings, as in bug bounty programs, companies benefit far more than they “lose.” | 
