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

6.3MEDIUM

Key Information:

Vendor

Python Software Foundation

Status
Cpython
Vendor
CVE Published:
3 June 2026

What is CVE-2026-3276?

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 Version(s)

CPython 0

References

https://mail.python.org/archives/list/security-announce@p...
vendor-advisory
https://github.com/python/cpython/pull/149080
patch
https://github.com/python/cpython/issues/149079
issue-tracking

CVSS V4

Score:
6.3
Severity:
MEDIUM
Confidentiality:
None
Integrity:
None
Availability:
Low
Attack Vector:
Network
Attack Complexity:
Low
Attack Required:
Physical
Privileges Required:
Undefined
User Interaction:
None

Timeline

  • Vulnerability published

  • Vulnerability Reserved

Credit

Seokchan Yoon (https://github.com/ch4n3-yoon)
Tim Peters (https://github.com/tim-one)
Bénédikt Tran (https://github.com/picnixz)
Serhiy Storchaka (https://github.com/serhiy-storchaka)
Stan Ulbrych (https://github.com/StanFromIreland)
Seth Larson (https://github.com/sethmlarson)
Petr Viktorin (https://github.com/encukou)
.