CVE-2026-5079
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 · uneditedImpact: multer versions 1.0.0 through 2.1.1 and 3.0.0-alpha.1 are vulnerable to a Denial of Service via deeply nested field names in multipart form data. The append-field dependency parses bracket notation in field names with no limit on nesting depth, allowing an attacker to force allocation of deeply nested object structures that consume CPU and memory. A single HTTP request with a crafted multipart body is sufficient to exploit this. Patches: Users should upgrade to multer 2.2.0 (2.x line) or 3.0.0-alpha.2 (3.x prerelease) and configure the new limits.fieldNestingDepth option to the minimum depth their application requires. Workarounds: Set limits.fields to a reasonable value to reduce the number of fields an attacker can send per request. This does not fully mitigate the issue but limits the impact.
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 confidencemulter's append-field dependency parses bracket notation in multipart form field names without limiting nesting depth, allowing attackers to craft requests with deeply nested field names (e.g., field[a][b][c][d]...) that cause excessive CPU and memory allocation leading to DoS.
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>= 1.0.0, < 2.2.0= 3.0.0CVSS 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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Check installed multer versionRun 'npm list multer' or check package.json dependencies to see the exact version installedAffected if The installed version is >= 1.0.0 and < 2.2.0, or exactly 3.0.0 (not 3.0.0-alpha.2 or later)
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Identify if multer handles multipart form uploadsSearch the codebase for multer() middleware usage, particularly looking for lines that initialize multer (e.g., 'var upload = multer()' or 'app.use(multer(...))')Affected if Multer is initialized and used to process multipart form data in the application
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Check if multipart endpoints are externally exposedReview routes or endpoints that use the multer middleware (e.g., upload.single(), upload.array(), upload.fields()) and determine if they accept incoming requests from untrusted sourcesAffected if Any route using multer middleware is accessible to external/unauthenticated users
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Verify fieldNestingDepth limit configuration (if using patched version)If multer 2.2.0+ is installed, check multer configuration for the 'limits.fieldNestingDepth' option to see if it is setAffected if The limits.fieldNestingDepth option is not configured or is set to a very high value, allowing deeply nested field names
You are affected if your application runs a vulnerable multer version (>=1.0.0, <2.2.0 or exactly 3.0.0) and processes multipart form submissions from external sources without restrictive nesting depth limits.
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 · scoped2.2.0
Upgrade to multer 2.2.0 or 3.0.0-alpha.2 and configure the new limits.fieldNestingDepth option to match the minimum nesting depth required by the application.
multer 2.2.0 (2.x line stable) or 3.0.0-alpha.2 (3.x prerelease)
- Upgrade multer to version 2.2.0 (recommended stable release) or 3.0.0-alpha.2 (prerelease) using your package manager (e.g., npm install [email protected])
- After upgrading, configure the new limits.fieldNestingDepth option in your multer setup to the minimum depth your application requires to limit nested object structures
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation2.0 h
- Implementation2.0 h
- Testing2.0 h
- Review / QA1.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-5079 — 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-2026-5079 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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- Version or environment caveats, and links to real fixes
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