CVE-2026-113866 (CVSS 5.9)

Description

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.

Is your site exposed to CVE-2026-113866?

Run a free security scan — no signup, results in seconds.

CVSS v3.1 Score

5.9

MEDIUM

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

EPSS — Exploit Prediction

0.0037

Probability of exploitation

0.30%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-523 CWE-523

References

Other References

https://bugzilla.mozilla.org/show_bug.cgi?id=2080121 https://www.mozilla.org/security/advisories/mfsa2026-114/ https://www.mozilla.org/security/advisories/mfsa2026-115/

Frequently Asked Questions

What is CVE-2026-113866? +

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. It has a CVSS v3.1 base score of 5.9 (MEDIUM).

How severe is CVE-2026-113866? +

CVE-2026-113866 has a CVSS v3.1 score of 5.9 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance. The EPSS score is 0.0037, placing it in the 0th percentile for exploitation probability.

How do I check if I'm vulnerable to CVE-2026-113866? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

Related Vulnerabilities

CVE-2024-4188

Unprotected Transport of Credentials vulnerability in OpenText™ Documentum™ Server could allow Credential Stuffing.This issue affects Documentum™ Server: from 16.7 through …

CVE-2024-1509 9.1

Brocade ASCG before 3.2.0 Web Interface is not enforcing HSTS, as defined by RFC 6797. HSTS is an optional response …

CVE-2025-57800 8.8

Audiobookshelf is an open-source self-hosted audiobook server. In versions 2.6.0 through 2.26.3, the application does not properly restrict redirect callback …

CVE-2025-64309 8.6

Brightpick Mission Control discloses device telemetry, configuration, and credential information via WebSocket traffic to unauthenticated users when they connect to …

CVE-2025-66029 7.6

Open OnDemand provides remote web access to supercomputers. In versions 4.0.8 and prior, the Apache proxy allows sensitive headers to …

CVE-2025-64308 7.5

The Brightpick Mission Control web application exposes hardcoded credentials in its client-side JavaScript bundle.

CVE-2026-113866