HTTP header injection via unvalidated control characters
Published Jan 20, 2026 · Updated Jan 20, 2026
HTTP header injection in affected CPython wsgiref releases allows remote authenticated users to inject response headers. Headers._convert_string_type accepts C0 controls in header names, values, and parameters before Headers serializes them into HTTP response lines. Exploitation requires a network application to pass attacker-controlled strings to this API with high-privileged access; injected CR or LF characters can create or alter response headers.
Summary
What happened
HTTP header injection in affected CPython wsgiref releases allows remote authenticated users to inject response headers. Headers._convert_string_type accepts C0 controls in header names, values, and parameters before Headers serializes them into HTTP response lines. Exploitation requires a network application to pass attacker-controlled strings to this API with high-privileged access; injected CR or LF characters can create or alter response headers.
The record
- CVE
- CVE-2026-0865
- Published
- Jan 20, 2026
- Updated
- Jan 20, 2026
- Vendor
- Python Software Foundation
- Product
- CPython
- Classifications
- CWE-74, T1190
- Attack vector
- network
- Privileges
- admin
Timeline
How it unfolded
- Jan 20, 2026CVE publishedPublication date reported by the CVE source.
- Jan 20, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=0 <3.15.0
What conditions does exploitation require?
What is affected?
Published CVSS scores
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Attacks
What attackers are doing with it
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Weakness, pattern, technique
Public exploit references
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Technologies
Your stack
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Your stack
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