Python MultipartApplication · Fastapiexpert
CVE-2026-40347
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedPython-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.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidencePython-Multipart versions before 0.0.26 contain a denial of service vulnerability where parsing specially crafted multipart/form-data requests with large preamble or epilogue sections causes excessive resource consumption. The parser inefficiently processes these sections, allowing attackers to exhaust server resources.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data
Python MultipartApplication
< 0.0.26CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- None
- Availability
- Low
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Check if Python-Multipart is installedRun 'pip show python-multipart' or 'pip list | grep multipart' to see if the package is present in your environmentAffected if The package is not installed or not found, then this CVE does not apply to your environment
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Determine the installed versionRun 'pip show python-multipart' and note the Version field, or run 'python -c "import multipart; print(multipart.__version__)"'Affected if The installed version is before 0.0.26 (e.g., 0.0.25, 0.0.20, etc.)
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Identify if your application parses multipart/form-dataSearch your codebase for multipart imports such as 'from multipart import' or 'import multipart' and usage of parse_form or similar functions that handle file uploads or form dataAffected if Your application imports and uses Python-Multipart to parse multipart form data, making it exposed to the vulnerable parsing code
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Check for processing of untrusted multipart requestsReview your web application configuration to confirm it accepts multipart/form-data requests from clients, as this is the attack vector for the DoSAffected if Your service processes untrusted multipart/form-data requests from users or external clients
You are affected if Python-Multipart version 0.0.26 or later is NOT installed AND your application uses this library to parse multipart form data from external sources.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
dbcve · scoped0.0.26
Upgrade Python-Multipart to version 0.0.26 or later, which implements efficient boundary skipping and immediate epilogue discarding.
0.0.26
- Run `pip install python-multipart==0.0.26` or `pip install python-multipart>=0.0.26` to upgrade to the fixed version
- Verify the upgrade was successful by running `pip show python-multipart` and confirming the version is 0.0.26 or later
- Test your application to ensure multipart form parsing still functions correctly after the upgrade
Generated from the published advisory — verify against the referenced sources before acting.
Fix this in Python Multipart
Scoped from the published advisory
- Consultation1.0 h
- Implementation1.0 h
- Testing4.0 h
- Review / QA1.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,856.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-40347 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-40347 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
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