Medium severity · published Apr 17, 2026
CVE-2026-40347
Python-Multipart affected by Denial of Service via large multipart preamble or epilogue data
5.3
CVSS
0.4%
EPSS
No
On KEV
Description
Python-Multipart is a streaming multipart parser for Python. Versions prior to 0.0.26 have a denial of service vulnerability when parsing crafted `multipart/form-data` requests with large preamble or epilogue sections. Upgrade to version 0.0.26 or later, which skips ahead to the next boundary candidate when processing leading CR/LF data and immediately discards epilogue data after the closing boundary.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
None
Integrity
None
Availability
Low
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.4% · higher than 29% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
PY
python-multipart · Kludex
< 0.0.26 · source: vendor, NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-40347
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-40347
Product
https://github.com/Kludex/python-multipart/releases/tag/0.0.26
Vendor Advisory
https://github.com/Kludex/python-multipart/security/advisories/GHSA-mj87-hwqh-73pj
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