Bitcoin Core Fixes Bug That Let Peers Take Down Windows, Mac Nodes

Any connected peer was able to take down a Bitcoin node running on Windows, macOS or BSD, Bitcoin Core developers disclosed Wednesday, Oct. 28. Fixes shipped this week in versions 29.5, 30.4, 31.2 and 32.1.

It was one of three bugs published that day. Linux nodes aren't affected by this one.

A paused peer could keep sending

Bitcoin Core normally stops reading from a peer once that peer's data piles up past a limit. On non-Linux systems, a peer was able to slip past that pause by sending TCP "urgent" data, so the node kept queuing data until it ran out of memory. The project rates it medium severity and says a malicious peer "can trivially crash any Windows, macOS or BSD node it is connected to."

The second medium-severity bug let a peer that claimed not to support BIP 31 pings (an older connection check) grow a node's memory by up to 2MB an hour per inbound peer, or 5MB per outbound peer. Nodes running `-blocksonly` are much less exposed.

One flaw outlives the patch

The third bug, rated low, lets a miner corrupt the undo files nodes use to roll back blocks during a reorganization. On 64-bit machines the project calls it impractical: an attacker would need to mine roughly a month of the whole network's blocks. Nodes on 32-bit systems or storing blocks on FAT32 drives remain affected.

Two of the three bugs were first flagged by an automated scan using a large language model, part of Elias Rohrer's Project Loupe at Spiral, and validated by developer Gregory Sanders.

In our opinion: the date that stands out is Oct. 23. That's when the scan flagged the Windows and Mac bug, and patched releases were out four days later.