Tesseract.js OCR Missing File Type Validation

[Kirtan-pc]

User description

Description

Add server-side magic byte verification to the image upload validation in the AI chat endpoint. Previously, only the client-supplied Content-Type / data URI prefix was checked, which can be trivially spoofed. Now the actual decoded file bytes are compared against known image signatures using the file-type package.

Related Issue

Closes #873

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Documentation update (README, guides, comments)
• Style / UI change (no logic change)
• Code refactor (no behavior change)
• Test addition or update
• Breaking change (fix or feature that would cause existing functionality to change)

Problem

The validateAiImageDataUrl function in src/lib/ai/ai-image-validation.ts only validated the client-supplied data URI prefix:

const validMime = /^data:image\/(png|jpe?g|webp);base64,/.test(img);

A malicious client could send:

data:image/png;base64,<crafted TIFF/WebP/binary payload>

This spoofed data URI would pass validation, and the payload would be forwarded to Groq's vision API. While the primary risk here is resource waste and potential parser crashes rather than code execution, the lack of content verification violates defense-in-depth principles.

Fix

1. Magic byte verification (src/lib/ai/ai-image-validation.ts)

• Added validateMagicBytes() function that decodes the base64 payload and runs fileTypeFromBuffer() from the file-type package
• file-type reads the file's magic bytes (first 2-8 bytes) to determine the actual format:
  • PNG: 89 50 4E 47 0D 0A 1A 0A
  • JPEG: FF D8 FF
  • WebP: 52 49 46 46 xx xx xx xx 57 45 42 50 (RIFF....WEBP)
• Returns 422 IMAGE_MIME_MISMATCH if the declared MIME doesn't match the detected format
• Returns 422 INVALID_IMAGE_PAYLOAD if the bytes don't match any known format

2. validateAiImageDataUrl is now async

The function signature changed from:

export function validateAiImageDataUrl(imageBase64: unknown): AiImageValidationResult

to:

export async function validateAiImageDataUrl(imageBase64: unknown): Promise<AiImageValidationResult>

This is necessary because fileTypeFromBuffer returns a Promise.

3. Updated caller (src/app/api/ask-ai/route.ts)

The ask-ai route's inline regex check was replaced with a call to the shared validateAiImageDataUrl() function, so all validation (format, MIME, size, magic bytes) happens in one place.

Before (ask-ai route — inline regex only)

if (body.imageBase64 !== undefined) {
    const img = body.imageBase64 as string;
    const validMime = /^data:image\/(png|jpe?g|webp);base64,/.test(img);
    if (!validMime) {
        return NextResponse.json({ error: "..." }, { status: 422 });
    }
}

After (ask-ai route — full validation)

if (body.imageBase64 !== undefined) {
    const result = await validateAiImageDataUrl(body.imageBase64);
    if (!result.ok) {
        return NextResponse.json(
            { error: result.error, code: result.code },
            { status: result.status }
        );
    }
}

Files Changed

File	Change
src/lib/ai/ai-image-validation.ts	Added validateMagicBytes() using file-type package; validateAiImageDataUrl is now async
src/app/api/ask-ai/route.ts	Replaced inline regex validation with validateAiImageDataUrl() call
package.json	Added file-type dependency

How Has This Been Tested?

• Tested locally with npm run dev
• Verified TypeScript compilation (npx tsc --noEmit passes)
• Verified on mobile viewport (375px)
• Verified on desktop viewport (1440px)

Checklist

• I have tested my changes locally (npx tsc --noEmit)
• My code follows the existing code style (TypeScript, no any types)
• I have not introduced unrelated changes (each PR should address one issue)
• I have added comments where necessary
• My branch is up to date with main
• I have linked the related issue above
• Screenshots are included (if this is a UI change)

---

CodeAnt-AI Description

Reject spoofed image uploads in AI chat

What Changed

• Image uploads are now checked against their actual file contents, not just the file name or declared image type
• Uploads with mismatched or unrecognizable image data now fail with a clear error instead of being forwarded
• The AI chat endpoint now returns the specific validation error and status for invalid images

Impact

✅ Fewer rejected AI image requests later in the flow
✅ Clearer image upload errors
✅ Less chance of malformed files reaching vision requests

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⛔ Files ignored due to path filters (1)

• package-lock.json is excluded by !**/package-lock.json

📒 Files selected for processing (3)

• package.json
• src/app/api/ask-ai/route.ts
• src/lib/ai/ai-image-validation.ts

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[knoxiboy]

Closing because this issue is already implemented by PR #778

[github-actions]

This pull request has been closed because the requested features or bug fixes are already implemented in the repository.