---
title: Bitcoin Core 32.1, 31.2, 30.4 and 29.5 fix a bug that let any connected peer crash Windows, macOS and BSD nodes with TCP urgent data; two found by an LLM scan | ctxsec
url: https://ctxsec.com/items/bitcoin-core-32-1-tcp-urgent-oom-undo-overflow-fixes
description: ""
status: "official (Bitcoin Core security disclosures and releases, Oct 27-28)"
published: 2026-10-28
---

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[← Cybersecurity News](/news) · [markdown](/items/bitcoin-core-32-1-tcp-urgent-oom-undo-overflow-fixes.md)

official (Bitcoin Core security disclosures and releases, Oct 27-28)

2026-10-28

### Bitcoin Core 32.1, 31.2, 30.4 and 29.5 fix a bug that let any connected peer crash Windows, macOS and BSD nodes with TCP urgent data; two found by an LLM scan

The Bitcoin Core project disclosed three bugs fixed in versions 29.5, 30.4, 31.2 and 32.1.

- **TCP urgent data memory exhaustion (Medium):** on non-Linux platforms, the `select()` socket backend kept reading after a peer was paused when it saw "exceptional" socket events, so a malicious peer sending TCP out-of-band data could queue unlimited data. The project says this lets a peer "trivially crash any Windows, macOS or BSD node it is connected to". Linux nodes, which use `poll()`, are not affected.
- **Slow memory growth from paused pre-BIP31 peers (Medium):** a peer that claims not to support nonced pings can avoid the 20-minute ping disconnect and let its send queue grow without limit.
- **Undo file overflow (Low):** a miner could push an undo file past 4 GiB so 32-bit positions wrap, corrupting undo data and stopping nodes on a later reorg (or immediately on Windows and 32-bit systems). Fixed for 64-bit systems; 32-bit systems and nodes storing blocks on FAT32 remain affected.

The TCP urgent-data bug was found by an automated LLM scan in Elias Rohrer's Project Loupe at Spiral and validated by Gregory Sanders. **What to do:** upgrade nodes, putting Windows and macOS nodes with open inbound connections first, and verify release signatures.

Sources: [Bitcoin Core: Unbounded memory growth through TCP urgent data on non-Linux systems](https://bitcoincore.org/en/2026/10/28/disclose-tcp-oom/) · [Bitcoin Core: Slow unbounded memory growth on paused pre-BIP31 peers](https://bitcoincore.org/en/2026/10/28/disclose-fpausesend-oom/) · [Bitcoin Core: Undo file overflow under extreme conditions](https://bitcoincore.org/en/2026/10/28/disclose-undo-overflow/) · [Bitcoin Core 32.1 release notes](https://bitcoincore.org/en/2026/10/27/release-32.1/)