Value overflow incident (2010)

The August 2010 bug that let a transaction create about 184 billion bitcoin; Satoshi shipped 0.3.10 within hours and the good chain overtook the bad one at block 74,691.

Discovery

On 15 August 2010 a Bitcointalk user posted “Strange block 74638”, noting that the value out of the block was “quite strange”^[1]. Within the hour another thread, “overflow bug SERIOUS”, said the block used “an integer overflow to make a negative total transaction”, with two outputs of 92,233,720,368.54 BTC each^[2]. Satoshi later edited that post to add the download links for the 0.3.10 patch^[2].

Why it worked

The Bitcoin Wiki explains that the code checking transactions before they entered a block did not account for outputs so large that they overflowed when summed^[3]. Bitcoin Takeover's fork history puts the total at roughly 184 billion bitcoin^[4].

The fix and the reorganisation

A new client was published within five hours with a soft-forking rule rejecting output overflows and any output above 21 million BTC^[3]. Many unpatched nodes kept building on the bad chain until the good chain overtook it at height 74,691, after which every node accepted it^[3]. Block 74,691 on today's chain has a header time of 08:20:08 UTC on 16 August 2010^[5].

Classification

Bitcoin Takeover's soft-fork history calls the fix “a tightening”, so it counts the event as “a soft fork with an unusually violent activation”^[4]. See Hard fork vs soft fork.

References

1. primary“Strange block 74638”, Bitcointalk topic 822, 15 Aug 2010 [archived]
2. primary“overflow bug SERIOUS”, Bitcointalk topic 823, 15 Aug 2010 (edited by satoshi with the 0.3.10 patch link) [archived]
3. secondaryBitcoin Wiki, “Value overflow incident” (revision 61347) [archived]
4. btkBitcoin: All the Hard Forks and Soft Forks (BTCTKVR: Forks!) [archived]
5. primarymempool.space, Bitcoin block 74,691 (header time 2010-08-16 08:20:08 UTC) [archived]

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