CVE-2026-41319: MailKit is a cross-platform mail client library built on top of MimeKit

Q: How do I fix CVE-2026-41319?

mailkit: upgrade to 4.16.0. Exact commands for each OS are on this page.

Q: Is CVE-2026-41319 being exploited?

CVE-2026-41319 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-41319 affect?

CVE-2026-41319 affects mailkit. Severity is medium (CVSS 6.5). MailKit is a cross-platform mail client library built on top of MimeKit. A STARTTLS Response Injection vulnerability in versions prior to 4.16.0 allows a Man-in-the-Middle attacker to inject arbitrary protocol responses across the plaintext

Q: How urgent is CVE-2026-41319?

Priority 31/100. Public exploit reference

Routine

MEDIUM 6.5UPGRADE

CVE-2026-41319 is a medium-severity flaw (CVSS 6.5) affecting mailkit. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

MailKit is a cross-platform mail client library built on top of MimeKit. A STARTTLS Response Injection vulnerability in versions prior to 4.16.0 allows a Man-in-the-Middle attacker to inject arbitrary protocol responses across the plaintext-to-TLS trust boundary, enabling SASL authentication mechanism downgrade (e.g., forcing PLAIN instead of SCRAM-SHA-256). The internal read buffer in `SmtpStream`, `ImapStream`, and `Pop3Stream` is not flushed w

Why this priority

Public exploit reference

A fixed release or distro patch exists.

Risk facts

CVSS score	6.5 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	Required
EPSS exploit chance	0.2% (top 87%)
CISA exploited list	No
Weakness	CWE-74
Published	2026-04-24
Last modified	2026-10-26

Publisher (CNA): GitHub, Inc. · Vendor: jstedfast

Last updated 2026-10-26 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-04-24 04:16 UTCPublished CVE record published
2026-10-26 22:10 UTCUpdated Record last modified

jstedfast mailkit UPGRADE

Affected: < 4.16.0

Fixed in: 4.16.0

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy mailkit || rpm -q mailkit || mailkit --version

2. UPGRADE to 4.16.0 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade mailkit

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade mailkit

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-41319?

mailkit: upgrade to 4.16.0. Exact commands for each OS are on this page.

Is CVE-2026-41319 being exploited?

CVE-2026-41319 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-41319 affect?

CVE-2026-41319 affects mailkit. Severity is medium (CVSS 6.5). MailKit is a cross-platform mail client library built on top of MimeKit. A STARTTLS Response Injection vulnerability in versions prior to 4.16.0 allows a Man-in-the-Middle attacker to inject arbitrary protocol responses across the plaintext

How urgent is CVE-2026-41319?

Priority 31/100. Public exploit reference

References

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