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adm-zip: Decompression-bomb protection (fix for CVE-2026-39244) can be bypassed by declaring uncompressed size as 0

Type: advisorySource: OSV1 source record

**Affected package:** adm-zip (npm) **Affected version:** 0.6.0 ## Summary The fix shipped for CVE-2026-39244 (`methods/inflater.js`) caps zlib's decompression output via `maxOutputLength: expectedLength`, where `expectedLength` is read directly from the ZIP entry's attacker-controlled "uncompressed size" header field (`CENLEN`/`LOCLEN`). This cap is only applied when `expectedLength > 0`: ```js const option = version >= 15 && expectedLength > 0 ? { maxOutputLength: expectedLength } : {}; return zlib.inflateRawSync(inbuf, option); ``` If an attacker sets the declared uncompressed-size field to exactly **0**, this condition is false, `option` becomes `{}`, and no output cap is passed to zlib at all. Node then falls back to zlib's own internal default limit (several GB), so a small, highly-compressible payload can still be decompressed to a very large size in memory -- the same class of resource-exhaustion issue the original CVE addressed, just triggered differently. ## Steps to Reproduce 1. Build a ZIP archive containing one DEFLATE-compressed entry whose real content is highly redundant (e.g. several MB of a repeated byte, achieving close to the ~1032:1 theoretical raw-DEFLATE compression ratio). 2. Patch the entry's declared uncompressed-size fields (both the local file header copy and the central directory copy, 4-byte little-endian values) to `0`. The compressed bytes and CRC32 are left untouched -- CRC validation still passes because CRC is computed over the real decompre

Announced Group revision 1
Original source ↗

GHSA-rcw4-f5rp-g42v

Primary source · Revision 1

Imported from structured advisory data. Source references identify upstream records or fields; verify affected versions and your deployed configuration.

Security context

Source reference: osv:GHSA-rcw4-f5rp-g42v

adm-zip

Source reference: /affected/0/package/name

Affected versions
Not stated in this record
Fixed versions
0.6.1

Source reference: /affected/0/ranges

Prerequisites
Not stated in this record

Structured affected-version data

Original package identities and version rules from this source.

[
  {
    "ranges": [
      {
        "type": "SEMVER",
        "events": [
          {
            "introduced": "0"
          },
          {
            "fixed": "0.6.1"
          }
        ]
      }
    ],
    "package": {
      "name": "adm-zip",
      "purl": "pkg:npm/adm-zip",
      "ecosystem": "npm"
    },
    "database_specific": {
      "source": "https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/09/GHSA-rcw4-f5rp-g42v/GHSA-rcw4-f5rp-g42v.json",
      "last_known_affected_version_range": "<= 0.6.0"
    }
  }
]
Related CVEs
CVE-2026-92000

Source reference: /aliases

Publisher severity

high

Source reference: /database_specific/severity

Linked CVE context

These ratings describe the referenced vulnerabilities and products. They are not a severity rating for every application using this dependency.

Event
#31151 · Revision 1
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