Is CVE-2026-40347 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-40347 being exploited in the wild.

How severe is CVE-2026-40347?

Medium severity, with a CVSS score of 5.3, published 18 April 2026.

Which products and versions are affected?

python-multipart (PyPI) < 0.0.26, ECOSYSTEM:introduced=0,fixed=0.0.26.

Is there a fix for CVE-2026-40347?

Yes. python-multipart (PyPI): upgrade to 0.0.26 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

Am I affected by CVE-2026-40347?

Check whether you run Fastapiexpert Python-Multipart or python-multipart (PyPI) 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-2026-40347: python-multipart affected by Denial of Service via large multipart preamble or epilogue data

Q: Is there a fix for CVE-2026-40347?

Yes. python-multipart (PyPI): upgrade to 0.0.26 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

Q: Am I affected by CVE-2026-40347?

Check whether you run Fastapiexpert Python-Multipart or python-multipart (PyPI) 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-2026-40347 · Severity: medium · CVSS 5.3 · Published 2026-04-18

Python-Multipart is a streaming multipart parser for Python. Versions prior to 0.0.26 have a denial of service vulnerability when parsing crafted `multipart/form-data` requests with large preamble or epilogue sections. Upgrade to version 0.0.26 or later, which skips ahead to the next boundary candidate when processing leading CR/LF data and immediately discards epilogue data after the closing boundary.

Technologies: python-multipart (PyPI). Vendors: PyPI.

Quick answers

Is CVE-2026-40347 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-40347 being exploited in the wild.
How severe is CVE-2026-40347?: Medium severity, with a CVSS score of 5.3, published 18 April 2026.
Which products and versions are affected?: python-multipart (PyPI) < 0.0.26, ECOSYSTEM:introduced=0,fixed=0.0.26.
Is there a fix for CVE-2026-40347?: Yes. python-multipart (PyPI): upgrade to 0.0.26 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
Am I affected by CVE-2026-40347?: Check whether you run Fastapiexpert Python-Multipart or python-multipart (PyPI) 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

python-multipart (PyPI): upgrade to 0.0.26 or later
```
pip install "python-multipart>=0.0.26"
```

Affected products

Fastapiexpert Python-Multipart
python-multipart (PyPI) < 0.0.26, ECOSYSTEM:introduced=0,fixed=0.0.26

Identifiers

CVE-2026-40347
GHSA-mj87-hwqh-73pj
PYSEC-2026-3038

References

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