One of the world’s largest crypto networks has patched a bug that could have let an attacker print counterfeit crypto out of thin air and spend it like the real thing. According to a vulnerability disclosure report published on XRPL.org on Friday, an integer overflow in the XRP Ledger’s payment engine could have let one cheap, rigged transaction mint coins beyond the network’s fixed supply. It’s the latest of several money-printing bugs in crypto this year, including a Zcash flaw in June and a Liquid Network exploit last month that let attackers cash out unbacked coins for real bitcoin.

In terms of the technical details, here’s how the exploit would have worked. When one payment consumed many offers from the XRP Ledger’s built-in order book, the engine summed the XRP owed using 64-bit math with no overflow check. If the total got too large, it would wrap around to a tiny number, paying offer owners in full while charging the buyer almost nothing.

The disclosure report says the bug likely dates all the way back to 2015, when the current payment engine was written.

To turn a profit with this bug, an attacker would need just a few hundred accounts posting absurdly priced offers, one payment sweeping through them, and a few hundred dollars’ worth of XRP in refundable reserves plus fees. “An attacker could have created spendable XRP far beyond the total supply in a single validated transaction,” the disclosure report says. At the time of this writing, CoinGecko puts the value of XRP’s entire circulating supply at just under $88 billion .

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