# CVE-2025-3875: Sender Spoofing via Malformed From Header in Thunderbird

> Attackers can spoof sender addresses in Thunderbird by using malformed From headers, potentially misleading users about the email origin.

- **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:** 14 May 2025
- **Updated:** 13 Apr 2026
- **Also known as:** DEBIAN-CVE-2025-3875, GHSA-rg69-33g2-mp48, UBUNTU-CVE-2025-3875

## What is CVE-2025-3875?

CVE-2025-3875 is a high-severity vulnerability in Mozilla Thunderbird, published on 14 May 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Thunderbird parses addresses in a way that can allow sender spoofing in case the server allows an invalid From address to be used. For example, if the From header contains an (invalid) value "Spoofed Name  ", Thunderbird treats spoofed@example.com as the actual address. This vulnerability was fixed in Thunderbird 128.10.1 and Thunderbird 138.0.1.

Weakness: CWE-290 (Authentication Bypass by Spoofing)

## Which versions are affected by CVE-2025-3875?

It affects 1 product.


Products: Mozilla Thunderbird.

## How do I fix CVE-2025-3875?

Upgrade to a fixed version.

## Is CVE-2025-3875 being exploited?

There is no known exploitation of CVE-2025-3875 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-2025-3875 and fix it if it is affected.

What it is: CVE-2025-3875 is a high-severity vulnerability in Mozilla Thunderbird, published on 14 May 2025. 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-2025-3875 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-2025-3875/ (Markdown: https://insights.sbomify.com/CVE-2025-3875/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-3875
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-3875
- OSV: https://osv.dev/vulnerability/CVE-2025-3875

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-3875/
Summaries are generated and may contain mistakes; the official description above is the record.