# CVE-2019-11755: Security feature bypass in Thunderbird

> Attackers can spoof valid digital signatures on S/MIME emails, bypassing integrity checks in Thunderbird.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/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:** 27 Sep 2019
- **Updated:** 4 Aug 2024
- **Also known as:** DEBIAN-CVE-2019-11755, GHSA-42rq-cwg9-m583, MGASA-2019-0292, UBUNTU-CVE-2019-11755

## What is CVE-2019-11755?

CVE-2019-11755 is a high-severity vulnerability in Mozilla Thunderbird, published on 27 Sep 2019. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

A crafted S/MIME message consisting of an inner encryption layer and an outer SignedData layer was shown as having a valid digital signature, although the signer might have had no access to the contents of the encrypted message, and might have stripped a different signature from the encrypted message. Previous versions had only suppressed showing a digital signature for messages with an outer multipart/signed layer. This vulnerability affects Thunderbird < 68.1.1.

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

## Which versions are affected by CVE-2019-11755?

It affects 1 product.


Products: Mozilla Thunderbird.

## How do I fix CVE-2019-11755?

Upgrade to a fixed version.

## Is CVE-2019-11755 being exploited?

There is no known exploitation of CVE-2019-11755 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-2019-11755 and fix it if it is affected.

What it is: CVE-2019-11755 is a high-severity vulnerability in Mozilla Thunderbird, published on 27 Sep 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-2019-11755 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-2019-11755/ (Markdown: https://insights.sbomify.com/CVE-2019-11755/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2019-11755
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2019-11755
- OSV: https://osv.dev/vulnerability/CVE-2019-11755

---
From sbomify Insights: https://insights.sbomify.com/CVE-2019-11755/
Summaries are generated and may contain mistakes; the official description above is the record.