Description
Several buffer-growth sites in libmime performed size arithmetic in 32-bit types without overflow checks. On a sufficiently large message the growth guard could fail open, or the buffer could be reallocated smaller than required, and a subsequent memcpy would then write attacker-controlled data across adjacent heap allocations. This vulnerability was fixed in Thunderbird 158 and Thunderbird 153.6.
Affected products
| Vendor | Product | Affected | Fixed |
|---|---|---|---|
| Mozilla | Thunderbird | — | 153.6 |
Fixed in Linux distributions
Distributions backport fixes, so the version that fixes this vulnerability differs per release — upgrade to at least the version shown. From the distributions' security trackers and advisories.
Debian
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian 14 | thunderbird | No fix yet | — |
| Debian 13 | thunderbird | No fix yet | — |
| Debian 12 | thunderbird | No fix yet | — |
Ubuntu
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 26.10 | thunderbird | No fix yet | — |
| Ubuntu 26.04 LTS | thunderbird | No fix yet | — |
| Ubuntu 24.04 LTS | thunderbird | No fix yet | — |
| Ubuntu 22.04 LTS | thunderbird | No fix yet | — |
openSUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| openSUSE Tumbleweed | MozillaThunderbird | 153.6.0-1.1 | openSUSE-SU-2026:12339-1 |
Oracle Linux
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Oracle Linux 10 | thunderbird | 153.6.0-1.0.1.el10_2 | ELSA-2026-96079 |
| Oracle Linux 9 | thunderbird | 153.6.0-1.0.1.el9_8 | ELSA-2026-96081 |
Advisories 5
- WID-SEC-2026-4216 Mozilla Firefox, Firefox ESR, und Thunderbird: Mehrere Schwachstellen BSI CERT-Bund (WID) · Nov 12, 2026
- WID-SEC-2026-3942 Mozilla Firefox und Thunderbrid: Mehrere Schwachstellen BSI CERT-Bund (WID) · Nov 11, 2026
- ELSA-2026-96079 Important: thunderbird security update (Oracle Linux 10) Oracle Linux Security Advisories (ELSA) · Nov 9, 2026
- ELSA-2026-96081 Important: thunderbird security update (Oracle Linux 9) Oracle Linux Security Advisories (ELSA) · Nov 9, 2026
- openSUSE-SU-2026:12339-1 MozillaThunderbird-153.6.0-1.1 on GA media SUSE / openSUSE Security Updates · Oct 31, 2026