Bitcoin Core Patches Three Bugs, Including Non-Linux Node Crash

Bitcoin Core disclosed three vulnerabilities on Oct. 28 and released fixes in versions 29.5, 30.4, 31.2 and 32.1, including a flaw that lets a malicious peer crash Windows, macOS and BSD nodes.

The Bitcoin Core software lets operators independently validate the Bitcoin blockchain and includes a wallet. The project rates two memory-growth vulnerabilities as medium severity and a third, involving stored blockchain data, as low severity. The three advisories do not say whether exploitation has been observed.

For operators on the 29.x, 30.x and 31.x branches, the patched point releases are 29.5, 30.4 and 31.2, respectively. Version 32.1 is the latest release. Operators running earlier point releases in those branches should upgrade.

The non-Linux crash vulnerability lets a connected attacker send specially marked network traffic, known as TCP urgent data, to bypass limits on how much incoming data a node queues for processing. The queue can then grow without limit until the node runs out of memory. Linux is unaffected by this particular flaw because it uses a different mechanism to monitor network connections.

The second memory-growth bug lets a malicious peer pretend to use an old protocol that lacks modern ping messages, avoiding a timeout that would normally disconnect it. By delaying reads, the peer can make the node keep queuing announcements. Memory usage can grow by up to 2 MB per hour per inbound peer or 5 MB per hour per outbound peer. Nodes configured to relay only blocks are much less affected.

A Separate Storage Risk Remains

The third vulnerability concerns “undo” files, which store information needed to reverse blocks during a blockchain reorganization. A miner could force these files beyond size limits, corrupting data or shutting down affected nodes. Bitcoin Core calls exploitation impractical: on 64-bit systems, preparation would require mining several thousand specially constructed blocks, with additional precise conditions needed for a reorganization-based attack.

The fixes address that flaw on 64-bit systems, including Windows, but 32-bit systems and nodes storing blocks on a FAT32 filesystem remain affected. If undo data has already been corrupted, restarting is insufficient; recovery requires rebuilding the blockchain index with a fixed version.

The advisories credit an automated AI scan by Spiral’s Project Loupe with discovering all three issues, with Gregory Sanders validating the findings and reporting them to Bitcoin Core. The project classified all three as “easily discoverable.” Its disclosure policy calls for publishing fixes across maintained branches and an advisory without the usual embargo for that category.

To upgrade, operators should shut down Bitcoin Core completely before installing or replacing the software, according to the release instructions. Those notes also say versions 29.x and older have reached end of life and will no longer receive updates.