Displaying a message could load an attacker-chosen URL through an OpenPGP key attachment

When a message containing an OpenPGP key attachment was displayed, Thunderbird automatically loaded the attachment's content to offer importing the key. A sender could mark the attachment as an external attachment pointing to an arbitrary URL, which Thunderbird then loaded without any user interaction, bypassing remote content blocking. On Windows, a URL pointing to an attacker-controlled network share could leak the user's NTLM credentials. The NTLM credential leak only affects Thunderbird on Windows. On other operating systems, the issue allowed a remote request that bypassed remote content blocking. This vulnerability was fixed in Thunderbird 159 and Thunderbird 153.6.

Source published

27 Oct 2026 18:16:28 UTC

Source modified

27 Oct 2026 18:27:46 UTC

Observed here

27 Oct 2026 19:45:55 UTC

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