USN-4202-1

It was discovered that a specially crafted S/MIME message with an inner encryption layer could be displayed as having a valid signature in some circumstances, even if the signer had no access to the encrypted message. An attacker could potentially exploit this to spoof the message author. (CVE-2019-11755)

Multiple security issues were discovered in Thunderbird. If a user were tricked in to opening a specially crafted website in a browsing context, an attacker could potentially exploit these to cause a denial of service, bypass security restrictions, bypass same-origin restrictions, conduct cross-site scripting (XSS) attacks, or execute arbitrary code. (CVE-2019-11757, CVE-2019-11758, CVE-2019-11759, CVE-2019-11760, CVE-2019-11761, CVE-2019-11762, CVE-2019-11763, CVE-2019-11764)

A heap overflow was discovered in the expat library in Thunderbird. If a user were tricked in to opening a specially crafted message, an attacker could potentially exploit this to cause a denial of service, or execute arbitrary code. (CVE-2019-15903)