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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.

PUBLISHED Reserved 2026-02-26 | Published 2026-06-03 | Updated 2026-06-10 | Assigner PSF




MEDIUM: 6.3CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N

Problem types

CWE-407

Product status

Default status
unaffected

Any version before 3.13.14
affected

3.14.0 (python) before 3.14.6
affected

3.15.0a1 (python) before 3.15.0b2
affected

Credits

Seokchan Yoon (https://github.com/ch4n3-yoon) reporter

Tim Peters (https://github.com/tim-one) remediation reviewer

Bénédikt Tran (https://github.com/picnixz) remediation reviewer

Serhiy Storchaka (https://github.com/serhiy-storchaka) remediation reviewer

Stan Ulbrych (https://github.com/StanFromIreland) remediation reviewer

Seth Larson (https://github.com/sethmlarson) coordinator

Petr Viktorin (https://github.com/encukou) remediation reviewer

References

www.openwall.com/lists/oss-security/2026/06/03/15

mail.python.org/.../thread/PP5HB4K7727OBBM76KA2ILID76K3OZGZ/ vendor-advisory

github.com/python/cpython/pull/149080 patch

github.com/python/cpython/issues/149079 issue-tracking

github.com/...ommit/6b505d1f41f8f3ea0fe5a4786d3a8fff1875cfc0 patch

github.com/...ommit/991224b1e8311c85f198f6dd8208bf8cff7fc26f patch

github.com/...ommit/ba785b88add96acbf403d65cb157fb2743a33a32 patch

github.com/...ommit/c5512bd7c1dc28055660565275012766941d3066 patch

cve.org (CVE-2026-3276)

nvd.nist.gov (CVE-2026-3276)

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