CVE-2026-41319

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 when the underlying stream is replaced with `SslStream` during STARTTLS upgrade, causing pre-TLS attacker-injected data to be processed as trusted post-TLS responses. Version 4.16.0 patches the issue.

CVSS v3 6.5 MEDIUM

6.5^/10

CVSS v3 : MEDIUM

Vector :

Exploitability : 2.8 / Impact : 3.6

Attack Vector NETWORK

Attack Complexity LOW

Privileges Required NONE

User Interaction REQUIRED

Confidentiality Impact NONE

Integrity Impact HIGH

Availability Impact NONE

Scope UNCHANGED

References

Link	Resource
https://github.com/jstedfast/MailKit/security/advisories/GHSA-9j88-vvj5-vhgr	Exploit Vendor Advisory
https://github.com/jstedfast/MailKit/security/advisories/GHSA-9j88-vvj5-vhgr	Exploit Vendor Advisory

Configurations

Configuration 1 (hide)

cpe:2.3:a:jstedfast:mailkit:*:*:*:*:*:*:*:*

History

No history.

Information

Published : 2026-04-24 04:16

Updated : 2026-06-17 10:46

NVD link : CVE-2026-41319

Mitre link : CVE-2026-41319

CVE.ORG link : CVE-2026-41319

JSON object : View

Products Affected

jstedfast

mailkit

CWE

CWE-74

Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection')

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