What is the CVSS score of CVE-2026-28356?

CVE-2026-28356 has a CVSS 3.1 base score of 7.5 (High). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H. EPSS exploitation probability: 0.5%.

Which versions of Python are affected by CVE-2026-28356?

A high-severity denial-of-service vulnerability exists in the Python multipart library affecting any web application that processes file uploads or multipart form data.. A patch is available.

Is there a public PoC exploit available for CVE-2026-28356?

Yes, a public proof-of-concept exploit is available for CVE-2026-28356. Prioritise patching immediately. EPSS: 0.5%.

How to fix or mitigate CVE-2026-28356?

Within 24 hours: Inventory all applications and services using the Python multipart library and assess exposure to untrusted HTTP multipart requests. Within 7 days: Implement WAF rules to filter malicious multipart headers and restrict multipart upload sizes; consider temporarily disabling file upload features if business-critical. Within 30 days: Monitor vendor communications for patch availability; evaluate alternative libraries or apply code-level mitigations such as regex optimization or input validation; conduct penetration testing post-remediation.

Python CVE-2026-28356

HIGH

Inefficient Regular Expression Complexity (ReDoS) (CWE-1333)

2026-03-12 security-advisories@github.com

GHSA-p2m9-wcp5-6qw3

Python Denial Of Service

7.5

CVSS 3.1 · Vendor: github

Severity by source

Vendor (github) PRIMARY

7.5 HIGH

AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

SUSE

HIGH

qualitative

Red Hat

7.5 HIGH

qualitative

Primary rating from Vendor (github).

CVSS VectorVendor: github

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

None

Availability

High

Lifecycle Timeline

Re-analysis Queued

Apr 16, 2026 - 14:52 vuln.today

cvss_changed

Patch released

Mar 31, 2026 - 21:13 nvd

Patch available

PoC Detected

Mar 12, 2026 - 21:07 vuln.today

Public exploit code

Analysis Generated

Mar 12, 2026 - 19:57 vuln.today

CVE Published

Mar 12, 2026 - 17:16 nvd

HIGH 7.5

Blast Radius

ecosystem impact

† from your stack dependencies † transitive graph · vuln.today resolves 4-path depth

1 pypi packages depend on multipart (1 direct, 0 indirect)

Ecosystem-wide dependent count for version 1.3.0.

DescriptionCVE.org

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.

AnalysisAI

High severity vulnerability in Python multipart. 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.

Technical ContextAI

Vulnerability Type: Inefficient Regular Expression Complexity (ReDoS) (CWE-1333) CVSS 3.1: 7.5/10.0 — Attack Vector: Network | Complexity: Low | Privileges Required: None | User Interaction: None Attack Techniques: Denial Of Service Source: https://github.com/defnull/multipart