create-ecdh: browser ECDH skips key validation, leaking private keys

create-ecdh is a browserifiable implementation of Node.js crypto.createECDH. In versions 4.0.4 and below, the JavaScript implementation (browser.js, used by browser bundlers and on Node.js versions without a working native crypto.createECDH) did not validate peer public keys in ECDH.prototype.computeSecret or ECDH.prototype.setPublicKey. The peer point was multiplied by the local private key without checking that it was on the configured curve or in its prime-order subgroup. An attacker who can submit public keys to a party that reuses a static private key can perform an invalid-curve or small-subgroup attack and recover the private key modulo small factors, eventually recovering the full key via the Chinese Remainder Theorem. For the ed25519 and curve25519 curves, low-order points were also accepted, which could force a predictable shared secret. On modern Node.js, create-ecdh re-exports the native implementation, which is not affected. This issue is fixed in version 4.0.5.