CVE-2026-28356

ReDoS in multipart 1.3.0 - `parse_options_header()`

Published Mar 12, 2026 CVSS 3.1 · 7.5 High EPSS < 1% KEV · Not listed
Description
multipart is a fast multipart/form-data parser for python. Prior to 1.2.2, 1.3.1 and 1.4.0-dev, the parse_options_header() function in multipart.py uses a regular expression with an ambiguous alternation, which can cause exponential backtracking (ReDoS) when parsing maliciously crafted HTTP or multipart segment headers. This can be abused for denial of service (DoS) attacks against web applications using this library to parse request headers or multipart/form-data streams. The issue is fixed in 1.2.2, 1.3.1 and 1.4.0-dev.

Remediation

No solution or workaround provided in the CVE record

Tracking

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Advisories

Source ID Title
Debian DSA Debian DSA DSA-6161-1 multipart security update
Github GHSA Github GHSA GHSA-p2m9-wcp5-6qw3 multipart vulnerable to ReDoS in `parse_options_header()`
Ubuntu USN Ubuntu USN USN-8343-1 multipart vulnerability
History
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Type Values Removed Values Added
First Time appeared Defnull
Defnull multipart
Vendors & Products Defnull
Defnull multipart
Type Values Removed Values Added
Description multipart is a fast multipart/form-data parser for python. Prior to 1.2.2, 1.3.1 and 1.4.0-dev, the parse_options_header() function in multipart.py uses a regular expression with an ambiguous alternation, which can cause exponential backtracking (ReDoS) when parsing maliciously crafted HTTP or multipart segment headers. This can be abused for denial of service (DoS) attacks against web applications using this library to parse request headers or multipart/form-data streams. The issue is fixed in 1.2.2, 1.3.1 and 1.4.0-dev.
Title ReDoS in multipart 1.3.0 - `parse_options_header()`
Weaknesses CWE-1333
References
Metrics cvssV3_1

{'score': 7.5, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'}

Weaknesses

Sources

Status
PUBLISHED
Assigner
GitHub_M
Published
Updated
Aug 24, 2026, 12:07 PM
Reserved
Feb 26, 2026, 6:38 PM
Status
Deferred
Published
Mar 12, 2026, 5:16 PM
Modified
Aug 24, 2026, 1:17 PM
Severity
Important
Public date
Mar 12, 2026, 4:45 PM