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Bitcoin History Part 10: The 184 Billion BTC Bug
There was something unusual about Bitcoin block 74638. It was Core developer Jeff Garzik who first spotted it, commenting on the “quite strange” transaction outputs, which stood at 92233720368.54 BTC apiece. That wasn’t meant to happen. Within an hour, another forum user had started a thread titled “overflow bug serious” in which he implored “We need a fix asap.” It was Aug. 15, 2010, and Bitcoin had just encountered its biggest bug yet.
Bitcoin Encounters a Very Big Bug
Bitcoin had already endured at least four major bugs or vulnerabilities prior to the integer overflow bug that led to 184 billion BTC being created out of thin air. The Bitcoin wiki lists 40 bugs of varying degrees of severity, with the most recent discovered in February 2019. CVE-2010-5139, however, was unlike anything the Bitcoin community had ever encountered in 2010 — or has seen since.
The bug that Garzik, among others, uncovered in block 74638 was Bitcoin’s first inflation bug. Given that the cryptocurrency’s total supply is meant to be capped at 21 million, the addition of 184 billion coins was a major problem to put it mildly. An integer overflow had caused a negative total transaction value. As Bitcoin talk forum user Ifm explained:
Normally the inputs are equal to the outputs of a transaction. The exception is when there is a ‘fee’ charged for the transaction. The net allows anyone to voluntarily pay any amout for a fee. So when the sum was negative the difference from the input looked like a fee. It slipped thru all the checks.
An unknown attacker had discovered the bug and used it to generate a ridiculously high number of bitcoins. Had they set their sights on a more modest total, it is possible their exploit might have lain undiscovered for longer than the 90 minutes it took for the scheme to be spotted. Once discovered, it was inevitable that a patch would be rushed through, and so it came to pass. Within two hours of Common Vulnerability and Exposure 2010-5139 striking, Core developers Gavin Andresen and Satoshi Nakamoto were on the case, and the 184 billion BTC transaction was purged from block 74638.
Source from Bitcoin.com, author Kai Sedgwick
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