Vulnerability · Published Oct 20, 2026 · Assigned by mozilla
CVE-2026-113868Uninitialized memory disclosure and out-of-bounds read in POP3 and SMTP NTLM authentication
Medium 5.3
In plain English
A medium-severity out-of-bounds read 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 0.4% (higher than 37% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
When authenticating to a POP3 or SMTP server using NTLM, Thunderbird did not check whether the server's challenge was valid base64. A malicious server could send a challenge that caused Thunderbird to include uninitialized heap memory in its NTLM response, disclosing that memory to the server. A challenge consisting only of base64 padding also caused an out-of-bounds read, crashing Thunderbird. This affected accounts configured to use NTLM or GSSAPI authentication. The uninitialized memory disclosure only affected NTLM. This vulnerability was fixed in Thunderbird 158.0.1 and Thunderbird 153.5.1.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | thunderbird | 1:153.5.1esr-1~deb12u1 | DEBIAN-CVE-2026-113868 |
| Debian:13 | thunderbird | 1:153.5.1esr-1~deb13u1 | DEBIAN-CVE-2026-113868 |
| Debian:14 | thunderbird | no fix listed | DEBIAN-CVE-2026-113868 |
| Ubuntu:22.04:LTS | thunderbird | no fix listed | UBUNTU-CVE-2026-113868 |
| Ubuntu:24.04:LTS | thunderbird | no fix listed | UBUNTU-CVE-2026-113868 |
| Ubuntu:26.04:LTS | thunderbird | no fix listed | UBUNTU-CVE-2026-113868 |
| Ubuntu:26.10 | thunderbird | no fix listed | UBUNTU-CVE-2026-113868 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| Mozilla | Thunderbird | see references |
Weakness: CWE-125 · Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H