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Vulnerability · Published May 13, 2026 · Assigned by GitHub_M

CVE-2026-42561Python-Multipart: Denial of Service via unbounded multipart part headers

High 7.5

In plain English

A high-severity resource allocation without limits in python-multipart from Kludex. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.7% (higher than 55% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)7.5High
Exploit odds (30 days)0.7%top 45.2% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known

Official description

Python-Multipart is a streaming multipart parser for Python. Prior to 0.0.27, python-multipart has a denial of service vulnerability in multipart part header parsing. When parsing multipart/form-data, MultipartParser previously had no limit on the number of part headers or the size of an individual part header. An attacker could send a request with either many repeated headers without terminating the header block or a single very large header value, causing excessive CPU work before request rejection or completion. This vulnerability is fixed in 0.0.27.

Affected packages & fixed versions

EcosystemPackageFixed inAdvisory
Debian:12python-multipartno fix listedDEBIAN-CVE-2026-42561
Debian:13python-multipartno fix listedDEBIAN-CVE-2026-42561
Debian:14python-multipart0.0.32-1DEBIAN-CVE-2026-42561
PyPIpython-multipart0.0.27GHSA-pp6c-gr5w-3c5g
PyPIpython-multipart0.0.27PYSEC-2026-3039
Ubuntu:25.10python-multipartno fix listedUBUNTU-CVE-2026-42561
Ubuntu:26.04:LTSpython-multipartno fix listedUBUNTU-CVE-2026-42561
Ubuntu:26.10python-multipartno fix listedUBUNTU-CVE-2026-42561

Affected products (as reported)

VendorProductVersions
Kludex python-multipart < 0.0.27

Weakness: CWE-770, CWE-606 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

References