[MFSA-2021-30] Security Vulnerabilities fixed in Thunderbird 78.12

CVE-2021-29969: IMAP server responses sent by a MITM prior to STARTTLS could be processed (high)
If Thunderbird was configured to use STARTTLS for an IMAP connection, and an attacker injected IMAP server responses prior to the completion of the STARTTLS handshake, then Thunderbird didn't ignore the injected data. This could have resulted in Thunderbird showing incorrect information, for example the attacker could have tricked Thunderbird to show folders that didn't exist on the IMAP server.

CVE-2021-29970: Use-after-free in accessibility features of a document (high)
A malicious webpage could have triggered a use-after-free, memory corruption, and a potentially exploitable crash.
This bug only affected Thunderbird when accessibility was enabled.

CVE-2021-29976: Memory safety bugs fixed in Thunderbird 78.12 (high)
Mozilla developers Valentin Gosu, Randell Jesup, Emil Ghitta, Tyson Smith, and Olli Pettay reported memory safety bugs present in Thunderbird 78.11. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code.

CVE-2021-30547: Out of bounds write in ANGLE (high)
An out of bounds write in ANGLE could have allowed an attacker to corrupt memory leading to a potentially exploitable crash.