🔒 [Fix file upload spoofing vulnerability]

[NITISH-R-G]

🎯 What: Implemented robust file upload validation by inspecting magic bytes instead of blindly trusting client-provided mimetypes.
⚠️ Risk: Attackers could spoof file.type (e.g. upload an .exe disguised as a .pdf), bypassing rudimentary checks and executing potentially harmful content.
🛡️ Solution: Integrated the file-type library to asynchronously detect MIME types based on actual buffer content. Applied changes simultaneously across api/analyze.ts (Vercel) and server.ts (local dev) with a safe fallback mechanism for text-based formats (CSV, JSON, TXT).

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PR created automatically by Jules for task 14649357054211411820 started by @NITISH-R-G

Summary by Sourcery

Harden file upload handling by validating MIME types based on file content instead of trusting client-provided types.

New Features:

• Introduce a shared detectMimeType helper to infer MIME types from file buffers with safe fallbacks for text formats.

Bug Fixes:

• Prevent file upload spoofing by rejecting files whose detected MIME type is not in the allowed set across both local and Vercel analyzers.

Build:

• Add the file-type dependency to support content-based MIME detection.

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Project	Deployment	Actions	Updated (UTC)
intelli-credit-v2	Ready	Preview, Comment	Jul 12, 2026 10:22pm

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[sourcery-ai]

Reviewer's Guide

This PR hardens file upload validation by introducing server-side MIME type detection using magic bytes via the file-type library, and enforcing a shared allowlist across both the Vercel edge handler and local Express server.

Sequence diagram for server-side MIME detection and validation during file upload

sequenceDiagram
  actor User
  participant Client
  participant ApiAnalyze
  participant Limits
  participant FileTypeLibrary
  participant AnalysisCore

  User->>Client: Select files
  Client->>ApiAnalyze: POST /api/analyze (files)

  loop For each uploaded file
    ApiAnalyze->>Limits: detectMimeType(buffer, fallbackMimeType)
    Limits->>FileTypeLibrary: fileTypeFromBuffer(buffer)
    FileTypeLibrary-->>Limits: result
    alt result.mime exists
      Limits-->>ApiAnalyze: mimeType
    else
      alt [fallbackMimeType is text/* or application/json]
        Limits-->>ApiAnalyze: fallbackMimeType
      else
        Limits-->>ApiAnalyze: application/octet-stream
      end
    end

    ApiAnalyze->>Limits: isAllowedMimeType(mimeType)
    alt MIME type allowed
      ApiAnalyze->>AnalysisCore: runAnalysis(files, apiMode, bureauApiKey)
      AnalysisCore-->>ApiAnalyze: analysis
    else
      ApiAnalyze-->>Client: 415 Unsupported file type
    end
  end

  ApiAnalyze-->>Client: JSON response (analysis or error)

Loading

File-Level Changes

Change	Details	Files
Introduce shared, async MIME type detection based on file buffer content with a safe text-format fallback.	Add fileTypeFromBuffer-based detectMimeType helper to shared limits module. Return detected MIME type when available, otherwise fall back to trusted text/* or application/json client types. Default to application/octet-stream when neither detection nor safe fallback applies.	api/_lib/limits.ts
Apply server-side MIME validation to uploaded files in the local Express dev server, rejecting disallowed types early.	Replace direct use of f.mimetype with detectMimeType on the uploaded buffer. Check each resolved MIME type against isAllowedMimeType and return 415 with structured error when unsupported. Build the AnalyzeInputFile array only for files that pass MIME validation, preserving base64 encoding of buffers.	server.ts
Apply server-side MIME validation to uploaded files in the Vercel API handler using the shared detection helper.	Replace reliance on client-provided f.type with detectMimeType over the request body bytes plus a lowercase fallback. Validate each detected MIME type via isAllowedMimeType and return a 415 JSON error for unsupported types. Keep existing analysis flow unchanged for allowed files, using the detected MIME type for downstream logic.	api/analyze.ts
Add the file-type dependency to support buffer-based MIME detection.	Declare file-type runtime dependency in package.json. Update package-lock.json to include file-type and its transitive dependencies.	package.json package-lock.json

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[sonarqubecloud]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud