[notorious-d-e-v]

Summary

MetaMask can change binary Solana messages before signing, then return the original bytes with a signature that does not match. This signs the exact requested bytes, blocks transaction messages from message-only signing, and shows binary data accurately so applications and users can check what was signed.

Changes

• Decode Base64 directly to bytes for the shared single/batch signing helper. Preserve NUL bytes, invalid UTF-8 sequences, byte order marks, and Unicode text; return the exact signed message.
• Reject compiled Solana transaction messages at both approval rendering and the signing authority. Transaction signing continues through its existing confirmation and scanning flow. Filter impossible headers and use Kit’s version-specific transaction size limits so large ordinary text remains signable.
• Show the full Base64 payload with an explicit binary/hidden-data warning whenever text decoding would change or hide content. Keep valid Unicode and multiline text readable; show an escaped text preview alongside Base64 for hidden but byte-preserving UTF-8, including emoji sequences and CRLF. Add English and Spanish labels.
• Cover legacy, v0, and codec-supported v1 transaction rejection, single/batch errors, distinct hidden-byte displays, binary preservation, and existing text/sign-in fixtures.

Validation

• Full Solana package suite: 90 suites; 1,078 tests pass, 5 skipped, 1 todo. Coverage thresholds pass.
• Solana Snap build, package TypeScript check, changed-source ESLint, and changelog validation pass.
• An independent software-key reproduction confirms a compiled transfer message is refused by the fixed signing service and the previously identical NUL-byte displays now differ. No RPC or funded transaction is involved.
• Rebased onto current main release commit 80b21f6; all five PR commits are SSH-signed.

Review

Claude Fable 5.1 was rerun at xhigh effort after the transaction guard and display fixes. The final read-only review found no remaining actionable P0–P3 findings. All prior findings and follow-up regressions were addressed; tests and builds were run separately by the author.

References

Fixes #506. Its browser evidence independently verifies the wallet-returned signature against converted bytes rather than the returned message. The regression tests use software keys; patched-extension and payment lifecycle testing remain separate.

Checklist

• Updated tests and documentation
• Updated the package changelog
• Signed commits