Django URLParsing NFKC DoS via slow URLField on Windows <6.0.3/5.2.12/4.2.29
CVE-2026-25673 Published on March 3, 2026
Potential denial-of-service vulnerability in URLField via Unicode normalization on Windows
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.
Vulnerability Analysis
CVE-2026-25673 can be exploited with network access, and does not require authorization privileges or user interaction. This vulnerability is considered to have a low attack complexity. The potential impact of an exploit of this vulnerability is considered to have no impact on confidentiality and integrity, and a high impact on availability.
Timeline
Initial report received.
Vulnerability confirmed. 24 days later.
Security release issued. 11 days later.
Weakness Type
What is a Resource Exhaustion Vulnerability?
The software does not properly control the allocation and maintenance of a limited resource, thereby enabling an actor to influence the amount of resources consumed, eventually leading to the exhaustion of available resources.
CVE-2026-25673 has been classified to as a Resource Exhaustion vulnerability or weakness.
Products Associated with CVE-2026-25673
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Affected Versions
djangoproject Django:- Version 6.0 and below 6.0.3 is affected.
- Version 6.0.3 is unaffected.
- Version 5.2 and below 5.2.12 is affected.
- Version 5.2.12 is unaffected.
- Version 4.2 and below 4.2.29 is affected.
- Version 4.2.29 is unaffected.
Exploit Probability
EPSS (Exploit Prediction Scoring System) scores estimate the probability that a vulnerability will be exploited in the wild within the next 30 days. The percentile shows you how this score compares to all other vulnerabilities.