Re: PGP/MIME and S/MIME mail clients vulnerabilities

[Jakub Wilk <jwilk () jwilk net>]

https://lists.gnupg.org/pipermail/gnupg-users/2018-May/060315.html has 
more details:

"[...] HTML is used as a back channel to create an oracle for modified 
encrypted mails.  It is long known that HTML mails and in particular 
external links like <img href="tla.org/TAG"/> are evil if the MUA 
actually honors them (which many meanwhile seem to do again; see all 
these newsletters).  Due to broken MIME parsers a bunch of MUAs seem to 
concatenate decrypted HTML mime parts which makes it easy to plant such 
HTML snippets."

--
Jakub Wilk