Vulnerability in Mozilla Thunderbird

[ Description ]Official description

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.

[ 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

• CERT-FR28 Oct 2026CERTFR-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.

  CVE-2026-117907CVE-2026-117889CVE-2026-117988+177 more CVEs
• BSI CERT-Bund27 Oct 2026WID-SEC-2026-4216

  Mozilla Firefox, Firefox ESR, and Thunderbird: Multiple vulnerabilities Translated from German

  Risk highCVE-2026-117930CVE-2026-117957CVE-2026-117890+177 more CVEs

[ References ]References

• bugzilla.mozilla.org/show_bug.cgi
• www.mozilla.org/security/advisories/mfsa2026-121
• www.mozilla.org/security/advisories/mfsa2026-122