CVE-2026-113866
MEDIUMDescription
When setting up an account, Thunderbird's Exchange AutoDiscover lookup also queried the domain's AutoDiscover service over plain HTTP. Due to a bug, that unencrypted request included the credentials the user had entered, allowing a network attacker to obtain the user's password. This vulnerability was fixed in Thunderbird 158.0.1 and Thunderbird 153.5.1.
How to fix
TridentStack Control can deploy fixes like this automatically across your Windows, macOS, and Linux fleet. See how it works
Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.
CVSS v3 Vector
Exploitability
Impact
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
Exploit Intelligence
Low risk: more likely to be exploited than 30% of all known CVEs.
References
Related Vulnerabilities
Other CWE-523 vulnerabilities, ordered by exploit likelihood. View all
| CVE | Severity | CVSS | EPSS | Exploited | Fix |
|---|---|---|---|---|---|
| CVE-2023-28708 | Medium | 4.3 | 1.8% | - | Fix |
| CVE-2021-38460 | High | 7.5 | 1.8% | - | - |
| CVE-2020-25175 | Critical | 9.8 | 1.1% | - | - |
| CVE-2022-31805 | High | 7.5 | 1.0% | - | Fix |
| CVE-2024-1102 | Medium | 6.5 | 0.8% | - | Fix |
| CVE-2017-16731 | High | 8.8 | 0.7% | - | - |
Common questions
How do I fix CVE-2026-113866?
Upgrade thunderbird on debian 12 to 1:153.5.1esr-1~deb12u1 or later.
Is CVE-2026-113866 being actively exploited?
Not that we know of. CVE-2026-113866 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 0.36% is the estimated probability that it will be exploited in the next 30 days. That is higher than 30% of all scored CVEs.
How severe is CVE-2026-113866?
CVE-2026-113866 has a CVSS v3 base score of 5.9, rated medium. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.
What does CVE-2026-113866 affect?
Published advisories record a fix for thunderbird (Debian). Only products with a sourced advisory are listed, so treat this as what we can cite rather than a complete inventory.
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Markdown
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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-10-22.