CVE-2026-8159
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 · unedited[email protected] and lower versions are vulnerable to denial of service via regular expression backtracking in the Content-Disposition filename parameter parser. A crafted multipart upload with a long header value can cause regex matching to take seconds, blocking the event loop. Impact: any service accepting multipart uploads via multiparty is affected. Workarounds: limiting upload sizes at the proxy or gateway layer reduces but does not eliminate the attack surface, since a small header of around 8 KB is sufficient to trigger the vulnerable backtracking. Upgrade to [email protected] or higher.
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 confidenceThe multiparty library versions 4.2.3 and below contain a vulnerable regular expression in the Content-Disposition filename parameter parser. Attackers can trigger catastrophic backtracking by sending crafted multipart uploads with long header values (~8KB), causing the regex matching to hang and block the Node.js event loop, resulting in denial of service.
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< 4.3.0CVSS 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
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
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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Identify multiparty installationRun 'npm list multiparty' or check package.json dependencies to see if multiparty is listed and note the installed versionAffected if The installed version is below 4.3.0 or no version is shown (meaning it may be a dev dependency or unresolved)
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Verify the application processes multipart uploadsSearch your codebase for 'form.parse' or 'multiparty.Form' usage, or look for middleware configurations that handle multipart form dataAffected if The application uses form.parse() to process file uploads, which triggers the vulnerable Content-Disposition parser
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Confirm filename handling is enabledInspect the multipart configuration options - look for whether 'uploadDir' or 'maxFieldsSize' options are set and whether incoming requests include Content-Disposition headers with filename parametersAffected if File uploads are accepted and the code processes the filename parameter from Content-Disposition headers
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Check for input size limitsReview your application code and any proxy/gateway configuration (load balancer, API gateway, nginx) for limits on request body size or individual field sizesAffected if No size limits are configured on uploaded file content or header fields, allowing the ~8KB crafted payloads to reach the vulnerable regex
You are affected if multiparty version is below 4.3.0 and your application processes multipart file uploads without request/header size restrictions.
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 · scoped4.3.0
Upgrade multiparty to version 4.3.0 or higher. As an additional layer of defense, implement upload size limits at the gateway/proxy layer to reduce the attack surface.
[email protected] or higher
- Run `npm list multiparty` to confirm the current installed version
- Run `npm install [email protected]` to install the fixed version, or run `npm update multiparty` to get the latest version
- Verify the upgrade was successful by running `npm list multiparty` and confirming the version is 4.3.0 or higher
- Rebuild and redeploy any services that use multiparty to apply the fix
- Test that multipart form uploads still function correctly after the upgrade
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation2.0 h
- Implementation2.0 h
- Testing4.0 h
- Review / QA2.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-8159 — 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-2026-8159 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
- No weaponised exploit code, or anything meant to cause harm
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