---
id: CVE-2024-12254
title: |-
  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"
summary: |-
  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 t…
severity: high
cvss: 7.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'
cwe:
  - CWE-400
  - CWE-770
  - CWE-770
published: '2024-12-06'
updated: '2026-07-31'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2024-12254'
references:
  - url: >-
      https://github.com/python/cpython/commit/71e8429ac8e2adc10084ab5ec29a62f4b6671a82
    label: cna@python.org
  - url: >-
      https://github.com/python/cpython/commit/9aa0deb2eef2655a1029ba228527b152353135b5
    label: cna@python.org
  - url: >-
      https://github.com/python/cpython/commit/e991ac8f2037d78140e417cc9a9486223eb3e786
    label: cna@python.org
  - url: 'https://github.com/python/cpython/issues/127655'
    label: cna@python.org
  - url: 'https://github.com/python/cpython/pull/127656'
    label: cna@python.org
  - url: >-
      https://mail.python.org/archives/list/security-announce@python.org/thread/H4O3UBAOAQQXGT4RE3E4XQYR5XLROORB/
    label: cna@python.org
  - url: 'http://www.openwall.com/lists/oss-security/2024/12/06/1'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: 'https://security.netapp.com/advisory/ntap-20250404-0010/'
    label: af854a3a-2127-422b-91ae-364da2661108
tags:
  - nvd
epss: 0.01868
epssPercentile: 0.78435
ingestedAt: '2026-07-31T15:59:52.064Z'
---

## Overview

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.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.