CVE-2024-12254: Python Software Foundation Cpython

High severity, CVSS 7.5. EPSS: 1.9% chance of exploitation in the next 30 days.

Starting in Python 3.12.0, the asyncio._SelectorSocketTransport.writelines() method would not "pause" writing and signal to the Protocol to drain the buffer to the wire once the write buffer reached the "high-water mark". Because of this, Protocols would not periodically drain the write buffer potentially leading to memory exhaustion. This vulnerability likely impacts a small number of users, you must be using Python 3.12.0 or later, on macOS or Linux, using the asyncio module with protocols, and using .writelines() method which had new zero-copy-on-write behavior in Python 3.12.0 and later. If not all of these factors are true then your usage of Python is unaffected.

Affected products

• Python Software Foundation Cpython: before 3.12.9 (fixed in 3.12.9); from 3.13.0, before 3.13.2 (fixed in 3.13.2); from 3.14.0a1, before 3.14.0a3 (fixed in 3.14.0a3); from 3.12.0, before 3.14.0a1 (fixed in 3.14.0a1)

Published 2024-12-06. Last modified 2026-07-31.