HTML injection via unneutralized closing script tag
Published Apr 22, 2026 · Updated Apr 22, 2026
HTML injection in CPython before 3.15.0 allows remote authenticated users to inject executable markup through a crafted cookie value. The http.cookies.Morsel.js_output() method places OutputString() inside an inline script while escaping only quotation marks, so a closing script tag terminates the element and exposes following markup to the HTML parser. Exploitation requires an application to render attacker-controlled cookie data through js_output(); the bounded consequence is JavaScript execution in the resulting page.
Summary
What happened
HTML injection in CPython before 3.15.0 allows remote authenticated users to inject executable markup through a crafted cookie value. The http.cookies.Morsel.js_output() method places OutputString() inside an inline script while escaping only quotation marks, so a closing script tag terminates the element and exposes following markup to the HTML parser. Exploitation requires an application to render attacker-controlled cookie data through js_output(); the bounded consequence is JavaScript execution in the resulting page.
The record
- CVE
- CVE-2026-6019
- Published
- Apr 22, 2026
- Updated
- Apr 22, 2026
- Vendor
- Python Software Foundation
- Product
- CPython
- Classifications
- CWE-150, T1059.007
- Attack vector
- network
- Privileges
- admin
Timeline
How it unfolded
- Apr 22, 2026CVE publishedPublication date reported by the CVE source.
- Apr 22, 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
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What is affected?
Published CVSS scores
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Attacks
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Weakness, pattern, technique
Public exploit references
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Technologies
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Your stack
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