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

> A malicious IMAP server can trigger a use-after-free to disclose heap memory, potentially persisting sensitive data to user preferences.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 1 Sep 2026
- **Updated:** 2 Sep 2026
- **Also known as:** DEBIAN-CVE-2026-84641, GHSA-f2hg-25f8-vgfj, UBUNTU-CVE-2026-84641

## 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 (Use After Free)

## Which versions are affected by CVE-2026-84641?

It affects 1 product.


Products: Mozilla Thunderbird.

## How do I fix CVE-2026-84641?

Upgrade to a fixed version.

## 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](https://insights.sbomify.com/CVE-2026-92238/): Ambiguous parsing of mail headers (critical 9.8)
- [CVE-2026-84637](https://insights.sbomify.com/CVE-2026-84637/): Calendar invitation attachments could launch local executables (critical 9.8)
- [CVE-2021-43529](https://insights.sbomify.com/CVE-2021-43529/): Memory corruption in Thunderbird (critical 9.8)
- [CVE-2019-11703](https://insights.sbomify.com/CVE-2019-11703/): Memory corruption in Thunderbird (critical 9.8)
- [CVE-2019-11704](https://insights.sbomify.com/CVE-2019-11704/): Memory corruption in Thunderbird (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-84641 and fix it if it is affected.

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

Affected product: Mozilla Thunderbird. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-84641/ (Markdown: https://insights.sbomify.com/CVE-2026-84641/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-84641
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-84641
- OSV: https://osv.dev/vulnerability/CVE-2026-84641

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-84641/
Summaries are generated and may contain mistakes; the official description above is the record.