Request-handling delays via inefficient multipart boundary scanning
Published Apr 17, 2026 · Updated Apr 17, 2026
Denial of service in Kludex python-multipart before 0.0.26 allows remote attackers to delay request handling via crafted multipart bodies. The parser inefficiently scans leading CR/LF bytes before the first boundary and continues processing epilogue data after the closing boundary, so oversized input drives excessive CPU work. Exposure requires an application to parse attacker-supplied multipart/form-data; the documented effect is reduced request capacity and delayed legitimate requests, not a complete application outage.
Summary
What happened
Denial of service in Kludex python-multipart before 0.0.26 allows remote attackers to delay request handling via crafted multipart bodies. The parser inefficiently scans leading CR/LF bytes before the first boundary and continues processing epilogue data after the closing boundary, so oversized input drives excessive CPU work. Exposure requires an application to parse attacker-supplied multipart/form-data; the documented effect is reduced request capacity and delayed legitimate requests, not a complete application outage.
The record
- CVE
- CVE-2026-40347
- Published
- Apr 17, 2026
- Updated
- Apr 17, 2026
- Vendor
- Kludex
- Product
- python-multipart
- Classifications
- CWE-400, CWE-834, T1499.003
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Apr 17, 2026CVE publishedPublication date reported by the CVE source.
- Apr 17, 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=< 0.0.26
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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