# CVE-2026-30227: MimeKit: CRLF Injection in Quoted Local-Part Enables SMTP Command Injection and Email Forgery

> Attackers can inject SMTP commands via CRLF in quoted email addresses, enabling email forgery or command execution in applications using MimeKit.

- **Severity:** Medium 6.9 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 6 Mar 2026
- **Updated:** 9 Mar 2026
- **Also known as:** GHSA-g7hc-96xr-gvvx

## What is CVE-2026-30227?

CVE-2026-30227 is a medium-severity command injection vulnerability in jstedfast MimeKit, published on 6 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

MimeKit is a C# library which may be used for the creation and parsing of messages using the Multipurpose Internet Mail Extension (MIME), as defined by numerous IETF specifications. Prior to version 4.15.1, a CRLF injection vulnerability in MimeKit allows an attacker to embed \r\n into the SMTP envelope address local-part (when the local-part is a quoted-string). This is non-compliant with RFC 5321 and can result in SMTP command injection (e.g., injecting additional RCPT TO / DATA / RSET commands) and/or mail header injection, depending on how the application uses MailKit/MimeKit to construct and send messages. The issue becomes exploitable when the attacker can influence a MailboxAddress (MAIL FROM / RCPT TO) value that is later serialized to an SMTP session. RFC 5321 explicitly defines the SMTP mailbox local-part grammar and does not permit CR (13) or LF (10) inside Quoted-string (qtextSMTP and quoted-pairSMTP ranges exclude control characters). SMTP commands are terminated by <CRLF>, making CRLF injection in command arguments particularly dangerous. This issue has been patched in version 4.15.1.

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

## Which versions are affected by CVE-2026-30227?

2 open source packages ship an affected version, including MimeKit. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `MimeKit` | NuGet | All versions | 4.15.1 |
| `MimeKit` | NuGet | All versions | 4.15.1 |

Products: Jstedfast Mimekit.

## How do I fix CVE-2026-30227?

Upgrade MimeKit to 4.15.1 or later.

## Is CVE-2026-30227 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-30227 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-30227 and fix it if it is affected.

What it is: CVE-2026-30227 is a medium-severity command injection vulnerability in jstedfast MimeKit, published on 6 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-30227 exists.

Affected packages and fixed versions:
- MimeKit (NuGet): affected all versions; fixed in 4.15.1
- MimeKit (NuGet): affected all versions; fixed in 4.15.1

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-2026-30227/ (Markdown: https://insights.sbomify.com/CVE-2026-30227/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-30227
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-30227
- OSV: https://osv.dev/vulnerability/CVE-2026-30227

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-30227/
Summaries are generated and may contain mistakes; the official description above is the record.