CVE-2026-3276Potential DoS via quadratic complexity in unicodedata.normalize()

Description

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.

Data: CVE.org, NVD, CISA KEV, FIRST EPSS, Ubuntu. Published as the sources state it, in English.

Affected products and versions

References and patches

• https://mail.python.org/archives/list/security-announce@python.org/thread/PP5HB4K7727OBBM76KA2ILID76K3OZGZ/ vendor-advisory
• https://github.com/python/cpython/pull/149080 patch
• https://github.com/python/cpython/issues/149079 issue-tracking
• https://github.com/python/cpython/commit/6b505d1f41f8f3ea0fe5a4786d3a8fff1875cfc0 patch
• https://github.com/python/cpython/commit/991224b1e8311c85f198f6dd8208bf8cff7fc26f patch
• https://github.com/python/cpython/commit/ba785b88add96acbf403d65cb157fb2743a33a32 patch
• https://github.com/python/cpython/commit/c5512bd7c1dc28055660565275012766941d3066 patch
• https://github.com/python/cpython/commit/90748760d38ca3ac5fc6788a69becab905c95598 patch
• https://github.com/python/cpython/commit/d3ab945af25b28dfe13ac6cb40c124a01b33ce1f patch
• https://github.com/python/cpython/commit/db744c0776c1d5dd11aaa70eff2a6993c408bacc patch
• https://github.com/python/cpython/commit/e322a1857084d521f79f45181b776f62e6acfc2c patch
• http://www.openwall.com/lists/oss-security/2026/06/03/15