HTTP Header Injection via Newlines in Python Headers

Publication date: 2026-01-20

Last updated on: 2026-03-03

Assigner: Python Software Foundation

Description

User-controlled header names and values containing newlines can allow injecting HTTP headers.

CVSS Scores

EPSS Scores

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Meta Information

Published

2026-01-20

Last Modified

2026-03-03

Generated

2026-07-06

AI Q&A

2026-01-21

EPSS Evaluated

2026-07-05

NVD

CVE-2026-0865

Affected Vendors & Products

Vendor	Product	Version / Range
python	cpython	3.10
python	cpython	3.11
python	cpython	3.12
python	cpython	3.13
python	cpython	3.14

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-74	The product constructs all or part of a command, data structure, or record using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify how it is parsed or interpreted when it is sent to a downstream component.

Attack-Flow Graph

Executive Summary

This vulnerability occurs when user-controlled HTTP header names and values include newline characters, which can be exploited to inject additional HTTP headers. This can lead to HTTP header injection attacks.

Impact Analysis

The vulnerability can allow attackers to manipulate HTTP headers, potentially leading to security issues such as response splitting, cache poisoning, or bypassing security controls, which can compromise the integrity and security of web applications.

Mitigation Strategies

To mitigate CVE-2026-0865, you should update your Python environment to a version where the fix has been applied (Python 3.10 through 3.14). The fix enforces validation in the wsgiref.headers.Headers module to reject any control characters, including newline characters, in HTTP header names and values. Applying the official patches or upgrading to a patched Python release will prevent exploitation of this header injection vulnerability. [1, 3]

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