What’s Vulnerable › Vulnerabilities

CVE-2024-12254: Unbounded memory buffering in SelectorSocketTransport.writelines()

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 1.9% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2024-12-06 · updated 2026-07-31
• Weakness: CWE-400

Description

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: from 3.12.0 before 3.14.0a1 — fixed in 3.14.0a1

How to fix

Upgrade to a fixed version: Python Software Foundation Cpython 3.14.0a1. Check the vendor advisory for mitigations.

References

• https://github.com/python/cpython/commit/71e8429ac8e2adc10084ab5ec29a62f4b6671a82
• https://github.com/python/cpython/commit/9aa0deb2eef2655a1029ba228527b152353135b5
• https://github.com/python/cpython/commit/e991ac8f2037d78140e417cc9a9486223eb3e786
• https://github.com/python/cpython/issues/127655
• https://github.com/python/cpython/pull/127656
• https://mail.python.org/archives/list/security-announce@python.org/thread/H4O3UBAOAQQXGT4RE3E4XQYR5XLROORB/
• http://www.openwall.com/lists/oss-security/2024/12/06/1
• https://security.netapp.com/advisory/ntap-20250404-0010/

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