CVE-2026-118177 is a vulnerability in Mozilla Thunderbird
Published on October 27, 2026
Calendar discovery accepted local file and remote network share locations
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.
Vulnerability Analysis
CVE-2026-118177 can be exploited with network access, and does not require authorization privileges or user interaction. This vulnerability is considered to have a low attack complexity. The potential impact of an exploit of this vulnerability is considered to have a high impact on confidentiality, with no impact on integrity, and a high impact on availability.
Weakness Type
What is an Open Redirect Vulnerability?
A web application accepts a user-controlled input that specifies a link to an external site, and uses that link in a Redirect. This simplifies phishing attacks. An http parameter may contain a URL value and could cause the web application to redirect the request to the specified URL. By modifying the URL value to a malicious site, an attacker may successfully launch a phishing scam and steal user credentials. Because the server name in the modified link is identical to the original site, phishing attempts have a more trustworthy appearance.
CVE-2026-118177 has been classified to as an Open Redirect vulnerability or weakness.
Products Associated with CVE-2026-118177
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Affected Versions
Mozilla Thunderbird:- Version 153.6, <= 153.* is unaffected.
- Version 159, <= * is unaffected.