CVE-2026-3276: Python Software Foundation Cpython

Medium severity, CVSS 6.3. EPSS: 0.5% chance of exploitation in the next 30 days.

unicodedata.normalize() can take excessive CPU time when processing specially crafted Unicode input containing long runs of combining characters with alternating Canonical Combining Class values. This affects all normalization forms.

Affected products

• Python Software Foundation Cpython: before 3.10.21 (fixed in 3.10.21); from 3.11.0, before 3.11.16 (fixed in 3.11.16); from 3.12.0, before 3.12.14 (fixed in 3.12.14); from 3.13.0, before 3.13.14 (fixed in 3.13.14); from 3.14.0, before 3.14.6 (fixed in 3.14.6); from 3.15.0a1, before 3.15.0b2 (fixed in 3.15.0b2)

Published 2026-06-03. Last modified 2026-08-13.