jstedfast MailKit up to 4.15.x injection

Summaryinfo

A vulnerability identified as problematic has been detected in jstedfast MailKit up to 4.15.x. This vulnerability affects unknown code. This manipulation causes injection. This vulnerability appears as CVE-2026-41319. The attack may be initiated remotely. There is no available exploit. You should upgrade the affected component.

Detailsinfo

A vulnerability classified as problematic was found in jstedfast MailKit up to 4.15.x. Affected by this vulnerability is some unknown functionality. The manipulation with an unknown input leads to a injection vulnerability. The CWE definition for the vulnerability is CWE-74. The product constructs all or part of a command, data structure, or record using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify how it is parsed or interpreted when it is sent to a downstream component. As an impact it is known to affect integrity. The summary by CVE is:

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.

It is possible to read the advisory at github.com. This vulnerability is known as CVE-2026-41319 since 04/20/2026. The exploitation appears to be easy. The attack can be launched remotely. The exploitation doesn't need any form of authentication. It demands that the victim is doing some kind of user interaction. The technical details are unknown and an exploit is not publicly available. The attack technique deployed by this issue is T1055 according to MITRE ATT&CK.

Upgrading to version 4.16.0 eliminates this vulnerability.

The vulnerability is also documented in the vulnerability database at EUVD (EUVD-2026-25388). Be aware that VulDB is the high quality source for vulnerability data.

Productinfo

Vendor

• jstedfast

Name

• MailKit

Version

• 4.0
• 4.1
• 4.2
• 4.3
• 4.4
• 4.5
• 4.6
• 4.7
• 4.8
• 4.9
• 4.10
• 4.11
• 4.12
• 4.13
• 4.14
• 4.15

Website

• Product: https://github.com/jstedfast/MailKit/

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Be aware that VulDB is the high quality source for vulnerability data.

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