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CVE-2026-77078 is an uncaught-exception vulnerability affecting Multer versions before 2.3.0, a Node.js middleware for processing multipart/form-data. Two specially crafted text-field names cause the append-field dependency to create a maximum-length sparse JavaScript array and then attempt to append another element. The resulting RangeError, indicating an invalid array length, escapes Multer's asynchronous field-processing flow and terminates the Node.js process. A small, remotely submitted multipart request can therefore cause denial of service. Multer 2.3.0 catches field-processing exceptions and returns an INVALID_FIELD_NAME middleware error instead of allowing the process to crash.
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1 valid exploit after Mallory filtered fakes, detection scripts, and README-only repos.
This 12-file TypeScript repository is an operational local proof of concept for CVE-2026-77078, an unauthenticated denial-of-service condition in Multer's multipart field-name processing. index.ts is the exploit client: it builds a raw multipart request with a maximum numeric array index followed by an append-style field name and POSTs it to 127.0.0.1:3000/upload. The src/ directory is a minimal NestJS target application: main.ts starts the app, app.module.ts loads UploadModule, and upload.controller.ts exposes POST /upload using NestJS FileInterceptor, a wrapper around Multer. The supplied package-lock resolves @nestjs/platform-express 11.2.5 and multer 2.2.0, an affected release. English and Russian Markdown files document the vulnerability, expected crash behavior, detection signals, and upgrade guidance to Multer 2.3.0 or later. The code contains no shell, persistence, data-exfiltration, or remote-code-execution payload; its sole capability is triggering process-level availability loss on an affected multipart endpoint.
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A remotely triggerable denial-of-service vulnerability in multer, a Node.js multipart/form-data middleware. Crafted field names create a maximum-length sparse array and then push beyond its limit, triggering an exception in the append-field dependency that multer does not catch. The Node.js process terminates. The listed CVSS v3 base score is 7.5, with no authentication or user interaction required. Upgrade to multer 2.3.0 or later.
A denial-of-service vulnerability in the npm multer package. Crafted multipart field names trigger an uncaught RangeError during field parsing, allowing a remote unauthenticated attacker to terminate the Node.js process with one request.
A high-severity unauthenticated remote denial-of-service vulnerability in Multer prior to 2.3.0. Crafted multipart field names can force an invalid JavaScript array-length operation, producing an uncaught RangeError and terminating the Node.js process.
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