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CVE-2026-28356— ReDoS in multipart 1.3.0 - `parse_options_header()`

Quick assessment

Affected
defnull multipart
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

python-multipart是Marcelo Trylesinski个人开发者的一个Python的流式多部分解析器。 python-multipart 1.2.2之前版本、1.3.1之前版本和1.4.0-dev之前版本存在安全漏洞，该漏洞源于parse_options_header函数使用存在歧义的正则表达式，可能导致解析恶意HTTP或多部分标头时出现指数级回溯，从而引发拒绝服务攻击。

CVSS 7.5 · High EPSS 1.07% · P64

Possible ATT&CK Techniques 1 AI

T1499 · Endpoint Denial of Service

Affected Version Matrix 2

VendorProduct Version RangeStatus
defnull multipart >= 1.3.0, < 1.3.1 affected
< 1.2.2 affected
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I. Basic Information for CVE-2026-28356

Vulnerability Information
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Vulnerability Title
ReDoS in multipart 1.3.0 - `parse_options_header()`
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
CWE-1333
Source: CVE Program / CVE List V5
Vulnerability Title
python-multipart 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
python-multipart是Marcelo Trylesinski个人开发者的一个Python的流式多部分解析器。 python-multipart 1.2.2之前版本、1.3.1之前版本和1.4.0-dev之前版本存在安全漏洞，该漏洞源于parse_options_header函数使用存在歧义的正则表达式，可能导致解析恶意HTTP或多部分标头时出现指数级回溯，从而引发拒绝服务攻击。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
defnull multipart >= 1.3.0, < 1.3.1 -

II. Public POCs for CVE-2026-28356

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III. Intelligence Information for CVE-2026-28356

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Vendor Advisories for CVE-2026-28356 (1)

IV. Related Vulnerabilities

Same weakness: CWE-1333

V. Comments for CVE-2026-28356

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