Inspection bypass via extended parameter decoding
Published Jun 22, 2026 · Updated Jun 22, 2026
Parameter smuggling in Kludex python-multipart before 0.0.30 allows remote attackers to bypass upstream multipart inspection. parse_options_header gives Content-Disposition and Content-Type values to email.message.Message, which decodes RFC 2231/5987 extended and continued parameters under bare name or filename keys and lets them override plain parameters. Exploitation requires multipart/form-data to traverse a differently interpreting upstream inspector; consequences are limited to application-specific field, filename, or upload-control bypass.
Summary
What happened
Parameter smuggling in Kludex python-multipart before 0.0.30 allows remote attackers to bypass upstream multipart inspection. parse_options_header gives Content-Disposition and Content-Type values to email.message.Message, which decodes RFC 2231/5987 extended and continued parameters under bare name or filename keys and lets them override plain parameters. Exploitation requires multipart/form-data to traverse a differently interpreting upstream inspector; consequences are limited to application-specific field, filename, or upload-control bypass.
The record
- CVE
- CVE-2026-53537
- Published
- Jun 22, 2026
- Updated
- Jun 22, 2026
- Vendor
- Kludex
- Product
- python-multipart
- Classifications
- CWE-436, CWE-20, T1190
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Jun 22, 2026CVE publishedPublication date reported by the CVE source.
- Jun 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?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=< 0.0.30
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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