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.
Weakness
An algorithm in a product has an inefficient worst-case computational complexity that may be detrimental to system performance and can be triggered by an attacker, typically using crafted manipulations that ensure that the worst case is being reached.
Affected Software
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Python3.13 | Ubuntu | upstream | * |
| Python3.14 | Ubuntu | devel | * |
| Python3.14 | Ubuntu | upstream | * |
References
- https://github.com/python/cpython/commit/6b505d1f41f8f3ea0fe5a4786d3a8fff1875cfc0
- https://github.com/python/cpython/commit/90748760d38ca3ac5fc6788a69becab905c95598
- https://github.com/python/cpython/commit/991224b1e8311c85f198f6dd8208bf8cff7fc26f
- https://github.com/python/cpython/commit/ba785b88add96acbf403d65cb157fb2743a33a32
- https://github.com/python/cpython/commit/c5512bd7c1dc28055660565275012766941d3066
- https://github.com/python/cpython/issues/149079
- https://github.com/python/cpython/pull/149080
- https://mail.python.org/archives/list/security-announce@python.org/thread/PP5HB4K7727OBBM76KA2ILID76K3OZGZ/
- http://www.openwall.com/lists/oss-security/2026/06/03/15