What’s Vulnerable › Vulnerabilities

CVE-2026-3298: Out-of-bounds write in Windows asyncio.ProacterEventLoop.sock_recvfrom_into() when using nbytes

• Severity: high (CVSS 8.8 v4.0)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.4% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-04-21 · updated 2026-10-26
• Weakness: CWE-787

Description

The method "sock_recvfrom_into()" of "asyncio.ProacterEventLoop" (Windows only) was missing a boundary check for the data buffer when using nbytes parameter. This allowed for an out-of-bounds buffer write if data was larger than the buffer size. Non-Windows platforms are not affected.

Affected products

• Python: before 3.11.16; from 3.12.0 before 3.12.14; from 3.13.0 before 3.13.14; from 3.14.0a1 before 3.14.5rc1; from 3.15.0a1 before 3.15.0b1 — fixed in 3.11.16, 3.12.14, 3.13.14, 3.14.5rc1, 3.15.0b1

How to fix

Upgrade to a fixed version: Python 3.11.16, 3.12.14, 3.13.14, 3.14.5rc1. Check the vendor advisory for mitigations.

References

• https://github.com/python/cpython/commit/1274766d3c29007ab77245a72abbf8dce2a9db4d
• https://github.com/python/cpython/commit/27522b7d6e6588f03e61099dd858cd5a9314e2f2
• https://github.com/python/cpython/commit/6c8b85b3f1d83d5697ec19880960e1eacee56688
• https://github.com/python/cpython/commit/95633d2aad4721e25e4dfd9f43dfb6e1edcbd741
• https://github.com/python/cpython/commit/f5ca38739241fe7a40a4b116d5a8a1364dd6fea7
• https://github.com/python/cpython/issues/148808
• https://github.com/python/cpython/pull/148809
• https://mail.python.org/archives/list/security-announce@python.org/thread/KWTPIQBOOOUNQP7UFSLBI437NJDFLA3F/

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