Should you update to Thunderbird 153?
No: install Thunderbird 159 instead. Thunderbird 153 is a security update Mozilla released on 21 Jul 2026 for Mac, Windows and Linux. It fixes 61 security flaws, 0 rated critical and 20 high by Mozilla.[1] None of them is known to be used in attacks.
It has since been replaced by Thunderbird 154, released 18 Aug 2026, which includes all of its fixes.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 153, so there’s no reason to stop at this one. Software Update offers the newest version your device can run.
Is Thunderbird 153 still safe?
Not any more. The 7 updates since, up to Thunderbird 159, fix 497 security flaws that Thunderbird 153 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 61 security flaws, 0 rated critical and 20 high by Mozilla.[1] The 20 critical and high ones are:
| Flaw | Severity | What Mozilla calls it |
|---|---|---|
CVE-2026-16349 | High | Same-origin policy bypass in the DOM: Navigation component |
CVE-2026-16350 | High | Incorrect boundary conditions in the Audio/Video: cubeb component |
CVE-2026-16362 | High | Use-after-free in the WebRTC: Audio/Video component |
CVE-2026-16351 | High | Sandbox escape due to use-after-free in the DOM: Navigation component |
CVE-2026-16352 | High | Sandbox escape due to use-after-free in the Disability Access APIs component |
CVE-2026-16363 | High | JIT miscompilation in the JavaScript: WebAssembly component |
CVE-2026-16364 | High | Incorrect boundary conditions in the Audio/Video: Playback component |
CVE-2026-16365 | High | Privilege escalation in the DOM: Workers component |
CVE-2026-16366 | High | Privilege escalation in the DOM: Navigation component |
CVE-2026-16353 | High | Invalid pointer in the DOM: Bindings (WebIDL) component |
CVE-2026-16354 | High | Information disclosure in the Graphics: ImageLib component |
CVE-2026-16367 | High | Sandbox escape due to invalid pointer in the Disability Access APIs component |
CVE-2026-16368 | High | Incorrect boundary conditions in the JavaScript: WebAssembly component |
CVE-2026-16369 | High | Integer overflow in the JavaScript: WebAssembly component |
CVE-2026-16355 | High | JIT miscompilation in the JavaScript Engine: JIT component |
CVE-2026-16356 | High | Sandbox escape due to use-after-free in the Disability Access APIs component |
CVE-2026-16357 | High | Incorrect boundary conditions in the Graphics component |
CVE-2026-16411 | High | Memory safety bugs fixed in Thunderbird 153 |
CVE-2026-16412 | High | Memory safety bugs fixed in Thunderbird ESR 140.13 and Thunderbird 153 |
CVE-2026-16360 | High | Memory safety bugs fixed in Thunderbird ESR 140.13 and Thunderbird 153 |
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 154 or later.
152.0.1 vs 153
Thunderbird 152.0.1, released 30 Jun 2026, fixed 2 security flaws. Thunderbird 153 fixes 61 security flaws and includes the fixes before it, so going straight to 153 gets you both.
- Before: Thunderbird 152.0.1, 30 Jun 2026, 2 security flaws
- After: Thunderbird 154, 18 Aug 2026, 56 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 2026-71”, 21 Jul 2026.