Vulnerability · Published Sep 30, 2026 · Assigned by mozilla
CVE-2026-103500Heap buffer overflow opening large email
Medium 6.3
In plain English
A medium-severity heap buffer 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 0.3% (higher than 20% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Severity (CVSS 3.1)6.3Medium
Exploit odds (30 days)0.3%top 79.8% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known
Official description
An attacker could cause a heap buffer overflow by getting a user to open an email that is greater than or equal to 2GB in size. This vulnerability was fixed in Thunderbird 157, Thunderbird 140.17, and Thunderbird 153.4.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | thunderbird | 1:140.17.0esr-1~deb12u1 | DEBIAN-CVE-2026-103500 |
| Debian:13 | thunderbird | 1:140.17.0esr-1~deb13u1 | DEBIAN-CVE-2026-103500 |
| Debian:14 | thunderbird | 1:153.4.0esr-1 | DEBIAN-CVE-2026-103500 |
| Ubuntu:22.04:LTS | thunderbird | no fix listed | UBUNTU-CVE-2026-103500 |
| Ubuntu:24.04:LTS | thunderbird | no fix listed | UBUNTU-CVE-2026-103500 |
| Ubuntu:26.04:LTS | thunderbird | no fix listed | UBUNTU-CVE-2026-103500 |
| Ubuntu:26.10 | thunderbird | no fix listed | UBUNTU-CVE-2026-103500 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| Mozilla | Thunderbird | see references |
Weakness: CWE-122 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:L