pako is a fast, pure-JavaScript port of zlib that handles gzip and deflate compression in the browser and Node.js, and it has a clean vulnerability record — the real security concern is not pako itself but how you handle untrusted compressed input, where a small archive can expand into a memory-exhausting payload. If you decompress data in the browser or need zlib behavior without a native module, pako is the standard choice, so it is worth knowing where the actual risk sits.
This review covers what pako does, its security profile, and the decompression-bomb problem that applies to any compression library.
What pako does
pako implements zlib's algorithms — deflate, inflate, gzip, and gunzip — in JavaScript. Because it is a port rather than a binding, it runs anywhere JavaScript runs, including the browser where a native zlib is not available. It is fast, modular so you can import only the deflate or inflate half, and it produces byte-for-byte results compatible with the reference zlib, which is why it shows up in everything from file-format parsers to network protocol implementations.
Typical usage is small:
const pako = require('pako');
// compress
const compressed = pako.deflate('some large string of text');
// decompress
const restored = pako.inflate(compressed, { to: 'string' });
The current major is 3.x, and it is the version you should be on for a new project.
Security profile: the port versus the original
There is an important distinction here that trips people up. The C zlib library has had notable CVEs over the years — CVE-2018-25032, a memory-corruption issue in the deflate path, is the well-known example. But pako is a reimplementation in JavaScript, not a wrapper around C zlib, so it does not automatically inherit zlib's native-code vulnerabilities. A buffer overflow in C does not translate to a JavaScript port that has no manual memory management.
That does not mean pako is provably flawless, but its own advisory record is clean, and it is actively maintained with a healthy release cadence. The takeaway: do not assume a zlib CVE headline applies to pako, and equally, do not assume pako is immune just because it is JavaScript. Track advisories against the pako package specifically. An SCA scanner will tell you if the exact version in your lockfile ever picks up an advisory, which is more reliable than reasoning about it from zlib news.
The real risk: decompression bombs
The security issue that actually matters with any compression library is the decompression bomb, sometimes called a zip bomb. Compression ratios can be enormous — a few kilobytes of highly repetitive input can expand into gigabytes of output. If you call pako.inflate() on attacker-controlled data without any limit, you hand an attacker a cheap way to exhaust your process's memory and crash it. This is not a flaw in pako; it is inherent to decompression, and it is your responsibility as the caller to bound it.
The defense is to cap output size as you decompress rather than after. pako supports streaming through its Inflate class, which lets you observe output incrementally and abort once you exceed a threshold:
const pako = require('pako');
function safeInflate(input, maxBytes) {
const inflator = new pako.Inflate();
let total = 0;
inflator.onData = (chunk) => {
total += chunk.length;
if (total > maxBytes) {
throw new Error('decompressed size exceeded limit');
}
};
inflator.push(input, true);
if (inflator.err) {
throw new Error(inflator.msg);
}
return inflator.result;
}
Set maxBytes to a realistic ceiling for your use case. The one-shot pako.inflate() is convenient for trusted data you produced yourself, but for anything crossing a trust boundary, the streaming form with a hard cap is the safe pattern.
Other safe-usage habits
Beyond bounding output, a few practices keep pako out of trouble.
Validate the input before you decompress where you can — check declared content length and reject implausibly small compressed payloads that claim to represent huge data. Treat decompression as work that happens inside a resource budget: if you decompress user uploads server-side, do it with memory and time limits and, ideally, in a worker so a runaway job cannot take down the main process. And keep pako current; being on the maintained 3.x line means you receive any fixes the maintainers ship.
Is pako well maintained and safe?
Yes on both counts. pako is a mature, widely depended-on library with a clean advisory history and steady maintenance, and there is no reason to avoid it. Just internalize the one thing that is genuinely your job: decompression of untrusted input must be bounded. Get that right and pako is a solid, safe choice. For more on defending the boundaries where untrusted data enters your app, the Safeguard Academy has relevant background.
FAQ
Is the pako npm package safe to use?
Yes. pako has a clean vulnerability record and is actively maintained on its 3.x line. The main security responsibility is not the library itself but bounding decompression of untrusted input, which is the caller's job with any compression tool.
Does pako inherit zlib's CVEs like CVE-2018-25032?
No, not automatically. pako is a pure-JavaScript reimplementation of zlib's algorithms, not a binding to the C library, so native memory-corruption issues such as CVE-2018-25032 do not translate to it. Track advisories against the pako package specifically rather than reasoning from zlib news.
What is a decompression bomb and how do I defend against it?
A decompression bomb is a small compressed payload that expands into an enormous output, exhausting memory. Defend by capping output size as you decompress — use pako's streaming Inflate class, tally the bytes emitted, and abort once you cross a realistic limit rather than decompressing everything first.
Which version of pako should I use?
Use the current 3.x major for new projects. Keeping to the maintained major line ensures you receive any fixes the maintainers publish and byte-compatible behavior with reference zlib.