Vulnerability · Published Oct 13, 2026 · Assigned by mozilla
CVE-2026-110247Integer overflow in libmime buffer growth could lead to heap corruption
High 8.4
In plain English
A high-severity integer overflow in Thunderbird from Mozilla. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 8% of all known vulnerabilities).
Official 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 packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | thunderbird | no fix listed | DEBIAN-CVE-2026-110247 |
| Debian:13 | thunderbird | no fix listed | DEBIAN-CVE-2026-110247 |
| Debian:14 | thunderbird | no fix listed | DEBIAN-CVE-2026-110247 |
| Ubuntu:22.04:LTS | thunderbird | no fix listed | UBUNTU-CVE-2026-110247 |
| Ubuntu:24.04:LTS | thunderbird | no fix listed | UBUNTU-CVE-2026-110247 |
| Ubuntu:26.04:LTS | thunderbird | no fix listed | UBUNTU-CVE-2026-110247 |
| Ubuntu:26.10 | thunderbird | no fix listed | UBUNTU-CVE-2026-110247 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| Mozilla | Thunderbird | see references |
Weakness: CWE-190 · Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H