HTTP header injection via unchecked cookie controls
Published Jan 20, 2026 · Updated Jan 20, 2026
CRLF injection in CPython http.cookies allows remote authenticated users to inject HTTP headers through crafted Morsel fields. Morsel.set, attribute assignment, setdefault, and BaseCookie.output accepted control characters without validating cookie names, values, or parameters before serializing HTTP headers. Exploitation requires an application to place attacker-controlled cookie data into Morsel fields and emit the resulting header, enabling unauthorized modification of HTTP messages.
Summary
What happened
CRLF injection in CPython http.cookies allows remote authenticated users to inject HTTP headers through crafted Morsel fields. Morsel.set, attribute assignment, setdefault, and BaseCookie.output accepted control characters without validating cookie names, values, or parameters before serializing HTTP headers. Exploitation requires an application to place attacker-controlled cookie data into Morsel fields and emit the resulting header, enabling unauthorized modification of HTTP messages.
The record
- CVE
- CVE-2026-0672
- Published
- Jan 20, 2026
- Updated
- Jan 20, 2026
- Vendor
- Python Software Foundation
- Product
- CPython
- Classifications
- CWE-93, T1190
- Attack vector
- network
- Privileges
- authenticated
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?
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- Affected versionversion=0 <3.15.0
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
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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