CVE-2026-84641 Information disclosure due to malicious IMAP server response

What is CVE-2026-84641?

CVE-2026-84641 is a high-severity use after free vulnerability in Mozilla Thunderbird, published on 1 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official description

A malicious IMAP server can trigger use-after-free and heap-memory disclosure by sending a crafted ID response. Heap contents can ultimately be persisted to prefs.js. This vulnerability was fixed in Thunderbird 155, Thunderbird 140.15, and Thunderbird 153.2.

Weakness: CWE-416

Which versions are affected by CVE-2026-84641?

It affects 1 product.

Products include Mozilla Thunderbird.

How do I fix CVE-2026-84641?

Upgrade to a fixed version.

Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.

Is CVE-2026-84641 being exploited?

There is no known exploitation of CVE-2026-84641 in the wild and no public exploit code.

Other vulnerabilities in Mozilla Thunderbird

• CVE-2026-92238 Ambiguous parsing of mail headers Critical 9.8
• CVE-2026-84637 Calendar invitation attachments could launch local executables Critical 9.8
• CVE-2021-43529 Memory corruption in Thunderbird Critical 9.8
• CVE-2019-11703 Memory corruption in Thunderbird Critical 9.8
• CVE-2019-11704 Memory corruption in Thunderbird Critical 9.8

All Mozilla Thunderbird vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as DEBIAN-CVE-2026-84641, GHSA-f2hg-25f8-vgfj, UBUNTU-CVE-2026-84641.