MimeKit has CRLF Injection in Quoted Local-Part that Enables SMTP Command Injection and Email Forgery

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

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 · score source

EPSS

• CVE-2026-30227: 1.21% estimated exploitation activity in the next 30 days; percentile 68.39 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary A CRLF Injection vulnerability in MimeKit 4.15.0 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. Details 1) RFC 5321 local-part grammar prohibits CR/LF in quoted-string RFC 5321 defines: When the local part is a quoted…

Published by the source

5 Mar 2026, 21:50 UTC

Last modified by the source

6 Mar 2026, 22:52 UTC

Source last checked

26 Oct 2026, 17:04 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-g7hc-96xr-gvvx

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# Patch Next advisory brief: CVE-2026-30227

Advisory: MimeKit has CRLF Injection in Quoted Local-Part that Enables SMTP Command Injection and Email Forgery
IDs: CVE-2026-30227, GHSA-g7hc-96xr-gvvx
Record: https://patchnext.com/advisories/cve-2026-30227 (revision 1, source checked 26 Oct 2026, 17:04 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.9)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: mimekit 4.15.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- NuGet mimekit: affected <= 4.15.0; fixed in 4.15.1

## Suggested inspection (read-only)
- NuGet mimekit: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on mimekit.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-g7hc-96xr-gvvx (GitHub-reviewed advisory GHSA-g7hc-96xr-gvvx lists affected ranges: NuGet mimekit >=0 <=4.15.0)

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