USN-4736-1: Thunderbird vulnerabilities

16 February 2021

Several security issues were fixed in Thunderbird.



  • thunderbird - Mozilla Open Source mail and newsgroup client


Multiple security issues were discovered in Thunderbird. If a user were
tricked into opening a specially crafted website in a browsing context,
an attacker could potentially exploit these to cause a denial of service,
obtain sensitive information, or execute arbitrary code. (CVE-2020-26976,
CVE-2021-23953, CVE-2021-23954, CVE-2021-23960, CVE-2021-23964)

It was discovered that responses received during the plaintext phase of
the STARTTLS connection setup were subsequently evaluated during the
encrypted session. A person in the middle could potentially exploit this
to perform a response injection attack. (CVE-2020-15685)

Update instructions

The problem can be corrected by updating your system to the following package versions:

Ubuntu 20.10

After a standard system update you need to restart Thunderbird to make
all the necessary changes.

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