An issue was discovered in Enigmail before 1.9.9. Signature spoofing is possible because the UI does not properly distinguish between an attachment signature, and a signature that applies to the entire containing message, aka TBE-01-021. This is demonstrated by an e-mail message with an attachment that is a signed e-mail message in message/rfc822 format.

An issue was discovered in Enigmail before 1.9.9. In a variant of CVE-2017-17847, signature spoofing is possible for multipart/related messages because a signed message part can be referenced with a cid: URI but not actually displayed. In other words, the entire containing message appears to be signed, but the recipient does not see any of the signed text.