Cookie output injection via incomplete control-character validation
Published Mar 16, 2026 · Updated Mar 16, 2026
Improper validation in CPython http.cookies allows remote authenticated users to inject control characters into generated cookie output. Morsel.update(), in-place union, and unpickling accepted unchecked values, while BaseCookie.js_output() emitted them without output validation. Reachability requires an application to pass attacker-controlled cookie state through an affected path; the resulting control characters can alter generated response data.
Summary
What happened
Improper validation in CPython http.cookies allows remote authenticated users to inject control characters into generated cookie output. Morsel.update(), in-place union, and unpickling accepted unchecked values, while BaseCookie.js_output() emitted them without output validation. Reachability requires an application to pass attacker-controlled cookie state through an affected path; the resulting control characters can alter generated response data.
The record
- CVE
- CVE-2026-3644
- Published
- Mar 16, 2026
- Updated
- Mar 16, 2026
- Vendor
- Python Software Foundation
- Product
- CPython
- Classifications
- CWE-116, CWE-20, T1190
- Attack vector
- network
- Privileges
- authenticated
Timeline
How it unfolded
- Mar 16, 2026CVE publishedPublication date reported by the CVE source.
- Mar 16, 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
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
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Technologies
Your stack
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Your stack
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