CVE-2026-84429: Potential denial-of-service vulnerability in HTTP header parsing

Vulnerability summary

CVE-2026-84429 is a medium (CVSS 6.9) Inefficient Algorithmic Complexity vulnerability in djangoproject django. EPSS estimates a 0.48% chance of exploitation in the next 30 days, higher than 41.6% of scored vulnerabilities.

Timeline

1. 06-10-2026
   PublishedVulnerability first disclosed.
2. 06-10-2026
   Last modifiedVulnerability information updated.

Description

An issue was discovered in Django 6.1 before 6.1.2, 6.0 before 6.0.9, and 5.2 before 5.2.18. `django.utils.http.parse_header_parameters()` was subject to a potential denial-of-service attack due to quadratic time complexity when parsing a value with many separators inside a quoted parameter. An unauthenticated request could reach this parsing through headers such as `Accept` or `Content-Type`, for instance via the content negotiation performed by `HttpRequest.accepts()`. The per-call length limit does not bound the combined size of repeated headers. Earlier, unsupported Django series (such as 5.1.x, 5.0.x, and 4.2.x) were not evaluated and may also be affected. Django would like to thank Jisung Chae for reporting this issue.

• CWE-407Inefficient Algorithmic ComplexityAn algorithm in a product has an inefficient worst-case computational complexity that may be detrimental to system performance and can be triggered by an attacker, typically using crafted manipulations that ensure that the worst case is being reached.