Cleartext Signed Message Signature Spoofing in openpgpjs

OpenPGP.js is a JavaScript implementation of the OpenPGP protocol. In affected versions OpenPGP Cleartext Signed Messages are cryptographically signed messages where the signed text is readable without special tools. These messages typically contain a "Hash: ..." header declaring the hash algorithm used to compute the signature digest. OpenPGP.js up to v5.9.0 ignored any data preceding the "Hash: ..." texts when verifying the signature. As a result, malicious parties could add arbitrary text to a third-party Cleartext Signed Message, to lead the victim to believe that the arbitrary text was signed. A user or application is vulnerable to said attack vector if it verifies the CleartextMessage by only checking the returned verified property, discarding the associated data information, and instead visually trusting the contents of the original message. Since verificationResult.data would always contain the actual signed data, users and apps that check this information are not vulnerable. Similarly, given a CleartextMessage object, retrieving the data using getText() or the text field returns only the contents that are considered when verifying the signature. Finally, re-armoring a CleartextMessage object (using armor() will also result in a "sanitised" version, with the extraneous text being removed. This issue has been addressed in version 5.10.1 (current stable version) which will reject messages when calling openpgp.readCleartextMessage() and in version 4.10.11…