Is CVE-2026-28356 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-28356 being exploited in the wild.

How severe is CVE-2026-28356?

High severity, with a CVSS score of 7.5, published 12 March 2026.

Which products and versions are affected?

multipart (PyPI) ECOSYSTEM:introduced=0,fixed=1.2.2,introduced=1.3.0,fixed=1.3.1, ECOSYSTEM:introduced=1.3.0,fixed=1.3.1; Red Hat AI Inference Server 3.2.

Is there a fix for CVE-2026-28356?

Yes. multipart (PyPI): upgrade to 1.3.1 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is CVE-2026-28356 attacked?

It is attacked over the network, in a software library.

Am I affected by CVE-2026-28356?

Check whether you run multipart (PyPI) or Red Hat AI Inference Server at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-28356: defnull multipart ReDoS in parse_options_header

CVE-2026-28356 · Severity: high · CVSS 7.5 · Published 2026-03-12

The 'multipart' Python library, used for processing web form data and file uploads, contains a flaw that can be triggered by specially crafted web requests. An attacker can send malicious HTTP headers that cause the server to consume excessive CPU resources, leading to a significant slowdown or complete service outage. This affects web applications and AI services that rely on this library to handle user-submitted data.

Technologies: Red Hat AI Inference Server. Vendors: PyPI, Red Hat.

Quick answers

Is CVE-2026-28356 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-28356 being exploited in the wild.
How severe is CVE-2026-28356?: High severity, with a CVSS score of 7.5, published 12 March 2026.
Which products and versions are affected?: multipart (PyPI) ECOSYSTEM:introduced=0,fixed=1.2.2,introduced=1.3.0,fixed=1.3.1, ECOSYSTEM:introduced=1.3.0,fixed=1.3.1; Red Hat AI Inference Server 3.2.
Is there a fix for CVE-2026-28356?: Yes. multipart (PyPI): upgrade to 1.3.1 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-28356 attacked?: It is attacked over the network, in a software library.
Am I affected by CVE-2026-28356?: Check whether you run multipart (PyPI) or Red Hat AI Inference Server at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

multipart (PyPI): upgrade to 1.3.1 or later
```
pip install "multipart>=1.3.1"
```

Technical details

A Regular Expression Denial of Service (ReDoS) vulnerability exists in the 'parse_options_header()' function within 'multipart.py'. The root cause is an ambiguous alternation in a regular expression that leads to exponential backtracking when processing maliciously crafted HTTP or multipart segment headers. A remote, unauthenticated attacker can exploit this by sending specially formatted requests, causing the application to hang for several seconds or longer as it consumes CPU cycles. This impact is particularly severe for WSGI and ASGI applications using 'multipart.parse_form_data()'. The issue is resolved in versions 1.2.2, 1.3.1, and 1.4.0-dev.

Affected products

defnull multipart < 1.2.2, >= 1.3.0 < 1.3.1, < 1.4.0-dev
Red Hat Red Hat OpenShift AI 2.25
Red Hat Red Hat AI Inference Server 3.2

Identifiers

CVE-2026-28356
GHSA-p2m9-wcp5-6qw3
PYSEC-2026-2670

Timeline

2026-03-12: disclosed: Initial advisory published by GitHub and defnull
2026-03-12: patched: Fixes released in versions 1.2.2 and 1.3.1
2026-03-25: advisory: Red Hat published security advisory RHSA-2026:5809

References

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