[ CVE-2026-118177 · Published 27 Oct 2026 ]
Vulnerability in Mozilla Thunderbird
[ Why it matters ]Priority signals
- Critical severity: CVSS 9.1
[ Description ]Official description
When looking for calendars in a directory on a server, during account setup or when adding a new network calendar, Thunderbird accepted calendar locations pointing to other servers, local files or network shares. A malicious server, or a network attacker when the lookup used plain HTTP, could make Thunderbird subscribe to such a location. On Windows this could leak the user's NTLM credentials to an attacker-controlled host on every calendar refresh, and changes to the calendar could be written to the attacker's share or overwrite a local file. This vulnerability was fixed in Thunderbird 159 and Thunderbird 153.6.
[ Fixes ]Fixes and patches
No fix or interim patch is linked from our sources yet. Check the vendor references below and limit exposure of affected systems until a fix is available.
[ Advisories ]Government CERT advisories
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CERT-FRCERTFR-2026-AVI-1406
Multiple vulnerabilities in Mozilla products Translated from French
Multiple vulnerabilities have been discovered in Mozilla products. Some of them allow an attacker to cause remote arbitrary code execution, privilege escalation and remote denial of service.
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BSI CERT-BundWID-SEC-2026-4216
Mozilla Firefox, Firefox ESR, and Thunderbird: Multiple vulnerabilities Translated from German