CVE-2025-64458 in Django
Summary
by MITRE • 11/05/2025
An issue was discovered in 5.1 before 5.1.14, 4.2 before 4.2.26, and 5.2 before 5.2.8. NFKC normalization in Python is slow on Windows. As a consequence, `django.http.HttpResponseRedirect`, `django.http.HttpResponsePermanentRedirect`, and the shortcut `django.shortcuts.redirect` were subject to a potential denial-of-service attack via certain inputs with a very large number of Unicode 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.
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Analysis
by VulDB Data Team • 12/30/2025
This vulnerability stems from a performance degradation in Python's Unicode normalization process on Windows systems, specifically affecting the NFKC normalization algorithm. The issue manifests when Django applications process HTTP redirects through HttpResponseRedirect, HttpResponsePermanentRedirect, or the redirect shortcut function. When these components encounter input containing a very large number of Unicode characters, the normalization process becomes computationally expensive and can lead to significant delays in response handling.
The technical flaw lies in how Django's redirect functionality internally utilizes Python's Unicode normalization capabilities during the processing of URL redirections. On Windows platforms, Python's implementation of NFKC normalization exhibits poor performance characteristics when dealing with large Unicode inputs, creating a potential attack vector for denial-of-service conditions. This performance degradation occurs because the normalization algorithm must process each Unicode character and its combining marks through multiple steps, resulting in exponential time complexity for inputs with many Unicode characters.
The operational impact of this vulnerability is significant for Django applications running on Windows servers that handle user-provided URLs or redirect parameters. Attackers can exploit this weakness by crafting malicious inputs with thousands or tens of thousands of Unicode characters, causing the application to spend excessive CPU cycles during redirect processing. This leads to resource exhaustion and can effectively render the application unresponsive to legitimate requests, particularly during high-traffic periods when the vulnerability can be amplified.
This vulnerability aligns with CWE-400, which addresses unchecked resource consumption, and relates to the broader category of denial-of-service attacks. The issue demonstrates how seemingly benign Unicode processing can become a security concern when combined with platform-specific performance characteristics. The ATT&CK framework categorizes this under T1499.004, specifically "Resource Hijacking: Network Denial of Service," as it consumes network and computational resources to prevent legitimate service usage. Organizations should implement input validation to limit the length of URL parameters and redirect targets, while also upgrading to patched versions of Django where available.
The vulnerability affects multiple Django versions including 5.1 before 5.1.14, 4.2 before 4.2.26, and 5.2 before 5.2.8, with earlier unsupported versions potentially also affected. The reported issue was discovered by Seokchan Yoon, highlighting the importance of community-driven security research in identifying platform-specific vulnerabilities. Organizations should prioritize patching their Django installations and consider implementing rate limiting or input sanitization measures as immediate mitigations while awaiting official updates.