Should you update to Thunderbird 156?
No: install Thunderbird 159 instead. Thunderbird 156 is a security update Mozilla released on 15 Sep 2026 for Mac, Windows and Linux. It fixes 75 security flaws, 0 rated critical and 28 high by Mozilla.[1] None of them is known to be used in attacks.
It has since been replaced by Thunderbird 157, released 30 Sep 2026, which includes all of its fixes.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 156, so there’s no reason to stop at this one. Software Update offers the newest version your device can run.
Is Thunderbird 156 still safe?
Not any more. The 4 updates since, up to Thunderbird 159, fix 336 security flaws that Thunderbird 156 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 75 security flaws, 0 rated critical and 28 high by Mozilla.[1] The 28 critical and high ones are:
| Flaw | Severity | What Mozilla calls it |
|---|---|---|
CVE-2026-92005 | High | Use-after-free in the Audio/Video: Web Codecs component |
CVE-2026-92006 | High | Privilege escalation due to incorrect boundary conditions in the Graphics: CanvasWebGL component |
CVE-2026-92007 | High | Privilege escalation due to incorrect boundary conditions in the Graphics: CanvasWebGL component |
CVE-2026-92008 | High | Privilege escalation due to incorrect boundary conditions in the Graphics: CanvasWebGL component |
CVE-2026-92009 | High | Privilege escalation due to incorrect boundary conditions in the Graphics: CanvasWebGL component |
CVE-2026-92010 | High | Privilege escalation due to incorrect boundary conditions in the Graphics: CanvasWebGL component |
CVE-2026-92011 | High | Privilege escalation due to incorrect boundary conditions in the Graphics: CanvasWebGL component |
CVE-2026-92012 | High | Privilege escalation due to incorrect boundary conditions in the Graphics: CanvasWebGL component |
CVE-2026-92013 | High | Privilege escalation due to incorrect boundary conditions in the Graphics: CanvasWebGL component |
CVE-2026-92015 | High | Privilege escalation in the WebExtensions component |
CVE-2026-92034 | High | Site isolation issue in the Graphics component |
CVE-2026-92035 | High | Sandbox escape due to incorrect boundary conditions in the Graphics component |
CVE-2026-92016 | High | Use-after-free in the Disability Access APIs component |
CVE-2026-92017 | High | Privilege escalation in the DOM: Service Workers component |
CVE-2026-92018 | High | Sandbox escape in the DOM: Core & HTML component |
CVE-2026-92019 | High | Mitigation bypass in the Remote Settings Client component |
CVE-2026-92020 | High | Privilege escalation due to incorrect boundary conditions in the Graphics: WebRender component |
CVE-2026-92022 | High | Use-after-free in the DOM: HTML Parser component |
CVE-2026-92023 | High | Use-after-free in the XML component |
CVE-2026-92024 | High | Use-after-free in the SVG component |
CVE-2026-92025 | High | Use-after-free in the DOM: Navigation component |
CVE-2026-92026 | High | Use-after-free in the Networking component |
CVE-2026-92036 | High | Incorrect boundary conditions in the Networking: HTTP component |
CVE-2026-92027 | High | Use-after-free in the DOM: Streams component |
CVE-2026-92028 | High | Use-after-free in the DOM: Core & HTML component |
CVE-2026-92029 | High | Use-after-free in the SVG component |
CVE-2026-92037 | High | Incorrect boundary conditions in the DOM: Animation component |
CVE-2026-92038 | High | Mitigation bypass in the Remote Settings Client 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 157 or later.
155 vs 156
Thunderbird 155, released 1 Sep 2026, fixed 30 security flaws. Thunderbird 156 fixes 75 security flaws and includes the fixes before it, so going straight to 156 gets you both.
- Before: Thunderbird 155, 1 Sep 2026, 30 security flaws
- After: Thunderbird 157, 30 Sep 2026, 76 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 2026-94”, 15 Sep 2026.