Summary adm-zip allocates an entry's output buffer from the declared uncompressed size (central-directory size field) before validating it against the actual data. A tiny crafted ZIP that declares a huge uncompressed size forces a multi-gigabyte allocation from a few bytes.

Impact On adm-zip 0.5.17 (latest), Node 24, a 105-byte ZIP with one stored entry declaring size = 1,774,399,200 makes new AdmZip(buf).getEntries()[0].getData() commit ~1.8 GB of resident memory in ~4.4 s before throwing Error: ADM-ZIP: CRC32 checksum failed, roughly 16 million times the input size. Because the buffer is committed before any validation, on a memory-constrained host (containers, serverless, small VMs) the allocation OOM-kills the process before the CRC check (uncatchable), and concurrent requests can exhaust memory even on larger hosts. Any service that reads entries from untrusted ZIPs is exposed to a remote denial of service.

Steps to reproduce Attachments are not supported in the advisory form, so the 105-byte PoC (sha256 980d34356fbb248fe527b9d0ac3eabc5c99393a374014be6199523de16709386) is inlined as base64 in this self-contained reproducer:

js const AdmZip = require('adm-zip'); // 105-byte crafted ZIP, base64-inlined // sha256 980d34356fbb248fe527b9d0ac3eabc5c99393a374014be6199523de16709386 const b64 = "UEsDBBQAAAAAAAAAAAAAAAAABQAAAAUAAAABAAAAYWhlbGxvUEsBAhQAFAAAAAAAAAAAAAAAAAAFAAAA4C7DaQEAAAAAAAAAAAAAAAAAAAAAAGFQSwUGAAAAAAEAAQAvAAAAJAAAAAAA"; const buf = Buffer.from(b64, "base64"); // 105 bytes const zip = new AdmZip(buf); zip.getEntries()[0].getData(); // commits ~1.8 GB, then throws "ADM-ZIP: CRC32 checksum failed"

The single entry declares uncompressed size = 1,774,399,200 with a compressed size of 5. getData() allocates the full declared size before the CRC check runs, so the memory is committed regardless of the (tiny) actual payload.

Root cause zipEntry.js does Buffer.alloc(<declared uncompressed size>) before checking the declared size against the compressed size / available bytes.

Suggested fix Validate the declared uncompressed size against the compressed size and a configurable maximum before allocating (yauzl, for example, requires the caller to bound this); reject or stream when the declared size is implausible relative to the input. Happy to send a patch.

adm-zip before 0.5.18 is vulnerable to denial of service via a crafted ZIP file with a manipulated uncompressed size header field. In zipEntry.js line 103, Buffer.alloc(centralHeader.size) allocates memory based on the declared uncompressed size from the ZIP central directory header without validating it against the actual compressed data size or imposing any upper bound. The size value is read directly from the binary header at entryHeader.js line 266 with no bounds check. An attacker can craft a ~120-byte ZIP file that declares ~4GB uncompressed size, causing a memory allocation amplification ratio of over 33 million to 1. The allocation occurs before CRC validation, so the malicious payload cannot be rejected early. All extraction and read methods are affected: readFile(), readAsText(), extractEntryTo(), extractAllTo(), extractAllToAsync(), test(), and entry.getData(). Any application accepting untrusted ZIP files via adm-zip is vulnerable to immediate process crash.

adm-zip 0.5.9 through 0.6.0 follows symbolic links at the extraction destination. Utils.sanitize in util/utils.js enforces containment by comparing only the string form of an archive entry name against the resolved extraction root, and Utils.writeFileTo opens the computed destination with fs.openSync(path, "w", 0o666), which resolves symbolic links and carries neither ONOFOLLOW nor a pre-write fs.lstatSync check. When a path component at the destination already exists as a symbolic link pointing outside the extraction root, extractAllTo, extractAllToAsync and extractEntryTo write the entry contents through that link and then chmod its target, placing attacker-controlled content in a file outside the root without any traversal sequence appearing in the archive. Reaching the write requires overwrite to be enabled, because the preceding fs.existsSync check also resolves the link and otherwise declines. An attacker able to create a symbolic link inside a shared, reused or predictable extraction directory, such as a temporary directory or a continuous integration workspace, can overwrite any file the extracting process is permitted to write.