Description

adm-zip: getDataAsync() bypasses the maxOutputLength size guard enforced by the synchronous getData() path

Summary

adm-zip enforces a maxOutputLength guard against decompression bombs on its synchronous getData() path, but the equivalent asynchronous getDataAsync() path does not enforce it — it accumulates and returns the entire decompressed output regardless of the entry's declared size. An application that checks an entry's declared size before deciding to process it, then reads the entry via getDataAsync() (a completely ordinary, often-recommended choice for I/O in Node.js), gets none of the protection it believes it has.

Details

methods/inflater.js:3-10 passes {maxOutputLength: expectedLength} to inflateRawSync, which Node enforces.

methods/inflater.js:12-31 passes the same option to createInflateRaw but never enforces it on the streaming path — it just accumulates every chunk and allocates a final Buffer of whatever size resulted.

PoC

const AdmZip = require('adm-zip');
const zip = new AdmZip();
zip.addFile('p', Buffer.alloc(64 * 1024 * 1024, 0x41)); // 64 MiB
const raw = Buffer.from(zip.toBuffer());
// patch the local + central declared uncompressed size to 1 byte
raw.writeUInt32LE(1, localHeaderSizeOffset);
raw.writeUInt32LE(1, centralHeaderSizeOffset);
const entry = new AdmZip(raw).getEntry('p');...
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Impact

An application that validates a declared size before reading an entry, then uses the async API, gets no protection against a high-ratio DEFLATE payload. Repeated or larger requests could contribute to memory exhaustion.

Mitigation

Aliases

References