crypto-js: Insufficient Entropy in Cryptographic Secret Generation via Vulnerable CryptoJS Dependency Chain

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 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 WordArray.random() behavior.
2. Enumerated the feasible outputs of the underlying PRNG.
3. Converted candidate entropy values into valid BIP39 recovery phrases.
4. Derived private keys and addresses across the relevant derivation paths and networks.
5. Compared derived addresses against public blockchain data.
6. Recovered the private keys controlling funded addresses.

Impact

An attacker can enumerate the reduced output space and recover security-sensitive values generated through the affected function.

Coinspect documented coordinated drain waves affecting addresses derived from vulnerable recovery phrases. As of July 13, 2026, the measured lower bound of stolen assets across the two events was approximately $5M.

The consequences are persistent:

• Updating an affected library or wallet does not strengthen a previously generated secret.
• Importing the same recovery phrase into an updated software or hardware wallet does not remediate the issue.