crypto-js is a JavaScript library of crypto standards. Versions of crypto-js prior to 4.0.0 generate randomness in CryptoJS.lib.WordArray.random() using a custom variation of the Multiply-With-Carry pseudorandom number generator, seeded from Math.random(), instead of a cryptographically secure source. This generator was introduced in version 3.1.2-4 and remained present in nearly every 3.x release. Nominal requests for 128 or 256 bits of entropy through this function produce effective search spaces of approximately 2 to the 39th and 2 to the 47th possibilities, small enough to enumerate on commodity hardware. Downstream wallet applications that used CryptoJS.lib.WordArray.random() as the entropy source for BIP39 recovery phrases are affected, and an attacker who enumerates the reduced output space can recover the resulting private keys and control the associated funds. This issue is fixed in version 4.0.0.

Affected: npm: crypto-js

### Summary

`CryptoJS.lib.WordArray.random()` in affected versions is not a cryptographically secure random number generator. Nominal requests for 128 or 256 bits of entropy produce effective search spaces of approximately 2^39 and 2^47 possibilities — small enough to enumerate on commodity hardware.

Coinspect's [Ill Bloom](https://www.coinspect.com/blog/ill-bloom-investigation/) investigation confirmed that downstream wallet applications used this function as the entropy source for BIP39 recovery phrases.

**An application is affected only if it uses the vulnerable function to generate security-sensitive values.**

Merely depending on `crypto-js < 4.0.0` is not sufficient to be exploitable.

### Details

The affected implementation used a custom variation of George Marsaglia's Multiply-With-Carry PRNG, seeded from `Math.random()`. It was introduced in 3.1.2-4 (June 2014, commit brix/crypto-js@ff1f003) in response to issue \#7, and was present in every 3.x release except 3.2.0 and 3.2.1. That **change was reverted in 3.3.0** because it was considered a breaking change, so projects tracking the 3.x line could resolve to newer versions that still contained the weak generator.

4.0.0 replaced the generator with the platform's native cryptographic API.

Applying PBKDF2, another KDF, or a cryptographic hash after the vulnerable generator does not restore missing entropy.

### Proof of concept

Coinspect reproduced the attack end to end:

1. Reimplemented the affected `WordArr…

Affected: Ubuntu:Pro:16.04:LTS: cryptojs, Ubuntu:Pro:18.04:LTS: cryptojs, Ubuntu:20.04:LTS: cryptojs, Ubuntu:Pro:22.04:LTS: cryptojs, Ubuntu:24.04:LTS: cryptojs

crypto-js is a JavaScript library of crypto standards. Versions of crypto-js prior to 4.0.0 generate randomness in CryptoJS.lib.WordArray.random() using a custom variation of the Multiply-With-Carry pseudorandom number generator, seeded from Math.random(), instead of a cryptographically secure source. This generator was introduced in version 3.1.2-4 and remained present in nearly every 3.x release. Nominal requests for 128 or 256 bits of entropy through this function produce effective search spaces of approximately 2 to the 39th and 2 to the 47th possibilities, small enough to enumerate on commodity hardware. Downstream wallet applications that used CryptoJS.lib.WordArray.random() as the entropy source for BIP39 recovery phrases are affected, and an attacker who enumerates the reduced output space can recover the resulting private keys and control the associated funds. This issue is fixed in version 4.0.0.