# CVE-2026-121946: zbateson mail-mime-parser before 3.0.9 and 4.x before 4.0.6 CRLF Header Injection via Message Builders


- **Severity:** Medium 6.9 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:N/SC:L/SI:L/SA:N`)
- **Exploited in the wild:** Not known
- **Fix available:** No
- **Published:** 4 Nov 2026
- **Updated:** 4 Nov 2026
- **Also known as:** GHSA-5gqw-c8wj-82xp, GHSA-gmgm-r6fh-fq6g

## What is CVE-2026-121946?

CVE-2026-121946 is a medium-severity vulnerability in zbateson mail-mime-parser, published on 4 Nov 2026. 

### Official description

zbateson mail-mime-parser before 3.0.9 and 4.x before 4.0.6 contains a CRLF header injection vulnerability in message-building helpers that fail to strip CR and LF characters. Attackers supplying crafted MIME type, charset, encoding, micalg, or protocol values can inject extra header lines such as a forged Bcc into outgoing messages.

Weakness: CWE-93 (Improper Neutralization of CRLF Sequences)

## Which versions are affected by CVE-2026-121946?


## How do I fix CVE-2026-121946?

No fix has been published for CVE-2026-121946 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-121946 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-121946 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-121946 and fix it if it is affected.

What it is: CVE-2026-121946 is a medium-severity vulnerability in zbateson mail-mime-parser, published on 4 Nov 2026. 
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-121946 exists.

Affected product: zbateson mail-mime-parser. 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-2026-121946/ (Markdown: https://insights.sbomify.com/CVE-2026-121946/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-121946
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-121946
- OSV: https://osv.dev/vulnerability/CVE-2026-121946

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-121946/
Summaries are generated and may contain mistakes; the official description above is the record.