# CVE-2018-18509: Security feature bypass in Thunderbird

> Attackers can forge valid S/MIME signatures on arbitrary email content, bypassing integrity checks in Thunderbird.

- **Severity:** Medium 5.3 (`CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/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:** 26 Apr 2019
- **Updated:** 5 Aug 2024
- **Also known as:** DEBIAN-CVE-2018-18509, GHSA-pqr9-248w-h9pf, UBUNTU-CVE-2018-18509

## What is CVE-2018-18509?

CVE-2018-18509 is a medium-severity vulnerability in Mozilla Thunderbird, published on 26 Apr 2019. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

A flaw during verification of certain S/MIME signatures causes emails to be shown in Thunderbird as having a valid digital signature, even if the shown message contents aren't covered by the signature. The flaw allows an attacker to reuse a valid S/MIME signature to craft an email message with arbitrary content. This vulnerability affects Thunderbird < 60.5.1.

Weakness: CWE-347 (Improper Verification of Cryptographic Signature)

## Which versions are affected by CVE-2018-18509?

It affects 1 product.


Products: Mozilla Thunderbird.

## How do I fix CVE-2018-18509?

Upgrade to a fixed version.

## Is CVE-2018-18509 being exploited?

There is no known exploitation of CVE-2018-18509 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-2018-18509 and fix it if it is affected.

What it is: CVE-2018-18509 is a medium-severity vulnerability in Mozilla Thunderbird, published on 26 Apr 2019. 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-2018-18509 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-2018-18509/ (Markdown: https://insights.sbomify.com/CVE-2018-18509/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2018-18509
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2018-18509
- OSV: https://osv.dev/vulnerability/CVE-2018-18509

---
From sbomify Insights: https://insights.sbomify.com/CVE-2018-18509/
Summaries are generated and may contain mistakes; the official description above is the record.