CVE-2026-84142
Published Sep 1, 2026
Modified Sep 1, 2026
Description
Internally found bugs present in Thunderbird 154. Some of these bugs showed evidence of memory corruption or another security-relevant defect and we presume that with enough effort some of these could have been exploited. This vulnerability was fixed in Firefox 155 and Thunderbird 155.
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References
Other References
https://bugzilla.mozilla.org/buglist.cgi?bug_id=2029421%2C2040889%2C2045313%2C2045435%2C2053578%2C2058621%2C2058626
https://bugzilla.mozilla.org/buglist.cgi?bug_id=2048796%2C2053150%2C2057356
https://www.mozilla.org/security/advisories/mfsa2026-82/
https://www.mozilla.org/security/advisories/mfsa2026-86/
Frequently Asked Questions
What is CVE-2026-84142? +
Internally found bugs present in Thunderbird 154. Some of these bugs showed evidence of memory corruption or another security-relevant defect and we presume that with enough effort some of these could have been exploited. This vulnerability was fixed in Firefox 155 and Thunderbird 155.
How do I check if I'm vulnerable to CVE-2026-84142? +
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.