Should you update to Thunderbird 158.0.1?
No: install Thunderbird 159 instead. Thunderbird 158.0.1 is a security update Mozilla released on 20 Oct 2026 for Mac, Windows and Linux. It fixes 8 security flaws, 0 rated critical and 5 high by Mozilla.[1] None of them is known to be used in attacks.
It has since been replaced by Thunderbird 159, released 27 Oct 2026, which includes all of its fixes. If you’re on an older version, install that instead.
Should you update?
No: install Thunderbird 159 instead. Thunderbird 159 came out on 27 Oct 2026 and includes every fix in Thunderbird 158.0.1, so there’s no reason to stop at this one. Software Update offers the newest version your device can run.
Is Thunderbird 158.0.1 still safe?
Not any more. Thunderbird 159 fixes 173 security flaws that Thunderbird 158.0.1 doesn’t, and each became public the day its fix shipped. Installing it is safe: get it only from Thunderbird’s own About window, or thunderbird.net, never from a link in an email, text or pop-up.
What it fixes
Mozilla lists 8 security flaws, 0 rated critical and 5 high by Mozilla.[1] The 5 critical and high ones are:
| Flaw | Severity | What Mozilla calls it |
|---|---|---|
CVE-2026-113866 | High | Account password sent unencrypted during Exchange account setup |
CVE-2026-113867 | High | Stanza injection in XMPP chat |
CVE-2026-113868 | High | Uninitialized memory disclosure and out-of-bounds read in POP3 and SMTP NTLM authentication |
CVE-2026-113399 | High | Incorrect boundary conditions in the SVG component |
CVE-2026-113470 | High | Cryptographic issue in the Security Block-lists, Allow-lists, and other State component |
How to update, and how long it takes
A minute or two. Thunderbird restarts and your mail stays where it was.
- Open Thunderbird.On a Mac choose Thunderbird → About Thunderbird; on Windows open the ☰ menu → Help → About Thunderbird.
- Let it download the update.The About window checks for one by itself; when it says “Restart to update Thunderbird”, click it.
To check it worked: The same About Thunderbird window shows the version under the name. It should say 159 or later.
158 vs 158.0.1
Thunderbird 158, released 13 Oct 2026, fixed 80 security flaws. Thunderbird 158.0.1 fixes 8 security flaws and includes the fixes before it, so going straight to 158.0.1 gets you both.
- Before: Thunderbird 158, 13 Oct 2026, 80 security flaws
- After: Thunderbird 159, 27 Oct 2026, 173 security flaws
- Thunderbird updates, every release and the latest version
- Updates, the latest version of everything HARD tracks
References
- ^ Mozilla. “Mozilla Foundation Security Advisory MFSA 2026-114”, 20 Oct 2026.