Affected versions of bip322 accepted a BIP-322 proof created with an attacker-controlled private key as a valid signature for an unrelated victim P2WPKH or P2SH-P2WPKH address, allowing complete authentication bypass in applications using verify simple, verify simple encoded, verify full, or verify full encoded as proof that a user controls a Bitcoin address.

In verify full, the verifier obtained the public key from the caller-controlled witness and passed it to verify full p2wpkh, where the supposed public-key mismatch check read the key from the same witness and compared it with itself:

let witness pub key = &witness.to vec()[1];

if &pub key.to bytes() != witness pub key {
  return Err(Error::PublicKeyMismatch);
}

Since pub key was originally parsed from that exact witness element, this comparison was tautological. The code verified that the signature was valid for the public key embedded in the witness, but never verified that this public key hashes to the claimed address, violating BIP-322's requirement that the message signature satisfy the message challenge (the claimed address's scriptPubKey).

As a result, an attacker could select any victim P2WPKH or P2SH-P2WPKH address, construct the BIP-322 challenge for that address and message, sign it with their own unrelated private key, and have the proof accepted. No victim key or victim interaction was required. Application-level nonces do not mitigate this, since the attacker can construct and sign the current challenge message with their own key.

P2TR verification is not affected: the public key is derived from the address's witness program rather than from the caller-controlled witness.

The flaw was corrected in commit e8accbe by deriving the expected scriptPubKey from the witness public key (P2WPKH(HASH160(pubkey)), wrapped in P2SH for the nested case) and requiring it to exactly equal the scriptPubKey of the claimed address before signature verification, failing with Error::PublicKeyMismatch otherwise. The fix is included in version 0.0.11. Affected versions 0.0.6 through 0.0.10 have been yanked from crates.io.

There is no known workaround that mitigates the vulnerability. Upgrading to version 0.0.11 is the recommended course of action.