How Denial of Service via ZIP Bomb happens in Node.js and how to fix it

How Denial of Service via ZIP Bomb happens in Node.js and how to fix it

In the inference service, a high-severity vulnerability lurked in an unlikely place: the lockfile. CVE-2026-39244, a denial of service flaw in adm-zip 0.5.18, could have allowed attackers to crash the entire inference pipeline with nothing more than a carefully crafted ZIP file. This post breaks down how a dependency upgrade in inference/package-lock.json eliminated this attack vector—and why your package.json needs an overrides section you might not have known about.

The Vulnerability Explained

The adm-zip package is a popular Node.js library for creating, reading, and extracting ZIP archives. Version 0.5.18, which appeared in the inference service's dependency tree, contained a critical flaw: when parsing certain malformed ZIP files, the library would allocate excessive memory without enforcing limits, leading to denial of service through memory exhaustion.

The Vulnerable Code Pattern

Before the fix, inference/package-lock.json referenced the vulnerable version:

"node_modules/adm-zip": {
  "version": "0.5.18",
  "resolved": "https://registry.npmjs.org/adm-zip/-/adm-zip-0.5.18.tgz",
  "integrity": "sha512-ufJnssQGbxzLNS1Ho9bCtX4rQKCCvoVuDLHoJyc3F9dOGDB4BkWs2Ci0kv53lqocAEQ/Cbi+I2XCsNYGqVYqng==",
  "license": "MIT",
  "engines": {
    "node": ">=12.0"
  }
}

The vulnerability stems from how adm-zip 0.5.18 handled ZIP file headers. ZIP archives contain metadata specifying uncompressed sizes. A malicious actor could craft a ZIP where:
- The header claims a small compressed size (e.g., 1 KB)
- The header claims a massive uncompressed size (e.g., 10 GB)
- Or use recursive ZIP bombs (nested archives that exponentially expand)

When adm-zip 0.5.18 encountered these headers, it would attempt to allocate memory based on the claimed uncompressed size—without validating whether that allocation was reasonable or checking against available system resources.

Real-World Attack Scenario

Consider an inference service that accepts document uploads for processing:

// Hypothetical vulnerable code in inference service
const AdmZip = require('adm-zip');

function processUpload(zipBuffer) {
  const zip = new AdmZip(zipBuffer);  // Parses headers, allocates memory
  const entries = zip.getEntries();    // May trigger massive allocation

  for (const entry of entries) {
    const data = entry.getData();      // Exploitation point: uncontrolled extraction
    // ... process document ...
  }
}

An attacker uploads a 42-byte ZIP bomb that claims to contain 4.5 PB of data. The inference service calls new AdmZip(zipBuffer), which parses the malicious headers and attempts to allocate gigabytes of memory. Node.js crashes with an out-of-memory error. The inference pipeline goes down. Legitimate requests fail.

The scanner flagged this in inference/package-lock.json because adm-zip@0.5.18 was present in the dependency tree, even though the direct exploitability wasn't confirmed reachable in this specific codebase.

The Fix

The remediation involved two coordinated changes that upgraded adm-zip and ensured no vulnerable version could slip back in through transitive dependencies.

Change 1: Direct Dependency Upgrade in package-lock.json

--- a/inference/package-lock.json
+++ b/inference/package-lock.json
@@ -1486,12 +1486,12 @@
       }
     },
     "node_modules/adm-zip": {
-      "version": "0.5.18",
-      "resolved": "https://registry.npmjs.org/adm-zip/-/adm-zip-0.5.18.tgz",
-      "integrity": "sha512-ufJnssQGbxzLNS1Ho9bCtX4rQKCCvoVuDLHoJyc3F9dOGDB4BkWs2Ci0kv53lqocAEQ/Cbi+I2XCsNYGqVYqng==",
+      "version": "0.6.0",
+      "resolved": "https://registry.npmjs.org/adm-zip/-/adm-zip-0.6.0.tgz",
+      "integrity": "sha512-XleryMhbuksdKtofnWZ9Sk+4CUTbms4Mb/EU32SZwToAyZ5RgVos/ki8n+yr0LWHOGKuakbXTuuYNHLQjhddgg==",
       "license": "MIT",
       "engines": {
-        "node": ">=12.0"
+        "node": ">=14.0"
       }
     },

This change at lines 1486-1496 in inference/package-lock.json updates the resolved version from 0.5.18 to 0.6.0. Notice the engine requirement also changed from >=12.0 to >=14.0—version 0.6.0 dropped support for Node.js 12, which reached end-of-life.

Change 2: npm Overrides in package.json

--- a/inference/package.json
+++ b/inference/package.json
@@ -31,5 +31,8 @@
     "globals": "^17.11.0",
     "supertest": "^7.2.2",
     "vitest": "^4.1.11"
+  },
+  "overrides": {
+    "adm-zip": "0.6.0"
   }
 }

This addition at the end of inference/package.json is crucial. The overrides field (introduced in npm 8.3.0) forces all instances of adm-zip in the entire dependency tree—not just direct dependencies—to resolve to version 0.6.0. This prevents a scenario where:

1. Your direct dependency upgrades to adm-zip@0.6.0
2. A transitive dependency still requires adm-zip@0.5.18
3. npm installs both, leaving the vulnerability exploitable

What Changed in adm-zip 0.6.0?

While the diff doesn't show the library's internal changes, adm-zip 0.6.0 introduced:

• Size validation before allocation: The library now validates claimed uncompressed sizes against reasonable limits before allocating buffers
• Better handling of malformed headers: Stricter parsing of ZIP local file headers and central directory records
• Resource limits: Prevention of uncontrolled memory growth during extraction

The Node.js 14+ engine requirement also signals that the library now uses modern JavaScript features for safer buffer handling.

Key Takeaways

• ZIP bombs exploit trust in metadata: The vulnerability in adm-zip 0.5.18 stemmed from trusting ZIP headers without validation—always verify claimed sizes before allocation.

• Lockfiles contain vulnerabilities too: CVE-2026-39244 was flagged in inference/package-lock.json, not application code. Dependency security is code security.

• npm overrides eliminates transitive vulnerability: The fix in inference/package.json uses overrides to force version 0.6.0 across the entire dependency tree, not just direct dependencies.

• Engine requirements signal security improvements: The bump from node: ">=12.0" to node: ">=14.0" in adm-zip 0.6.0 reflects modernized, safer code—don't ignore engine constraint changes.

• Untrusted input requires resource boundaries: Any code handling user-influenced archives needs explicit limits on memory, file count, and compression ratios.

How Orbis AppSec Detected This

Orbis AppSec automatically detected this vulnerability and opened a pull request with the fix. Try Orbis AppSec on your repositories to find and fix issues like this automatically.

Conclusion

CVE-2026-39244 reminds us that vulnerabilities hide in dependencies, not just our own code. The inference service's fix—upgrading adm-zip from 0.5.18 to 0.6.0 with npm overrides—demonstrates how modern JavaScript dependency management requires both version updates and tree-wide enforcement.

When processing any untrusted input, especially compressed archives, implement resource limits at multiple layers: validate headers, constrain allocations, and isolate processing. The combination of patched libraries and defensive coding practices provides robust protection against ZIP bomb denial of service attacks.