What is CVE-2026-28356?

CVE-2026-28356 is a high-severity vulnerability in Defnull Multipart, classified under Inefficient Regular Expression Complexity. CVSS score: 7.5/10. Published 2026-03-12.

How severe is CVE-2026-28356?

High severity. CVSS v3 base score is 7.5 out of 10.

Vulnerability in Defnull Multipart

CVE-2026-28356

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 backtr…

Vulnerability class: ReDoS (Regular Expression Denial of Service)

EPSS: 0.009 (75.4th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

Affected products

Defnull Multipart — versions >= 1.3.0, < 1.3.1, < 1.2.2

Weakness classification (CWE)

CWE-1333 — Inefficient Regular Expression Complexity

References

https://github.com/defnull/multipart/security/advisories/GHSA-p2m9-wcp5-6qw3 (x_refsource_CONFIRM)

Frequently asked questions

What is CVE-2026-28356?: CVE-2026-28356 is a high-severity vulnerability in Defnull Multipart, classified under Inefficient Regular Expression Complexity. CVSS score: 7.5/10. Published 2026-03-12.
How severe is CVE-2026-28356?: High severity. CVSS v3 base score is 7.5 out of 10.