CVE-2026-41319
MEDIUM EPSS 12.8%
Published Apr 24, 20262mo ago · Modified Jun 17, 20262w ago
5.9 CVSS 3.1
Published Apr 24, 2026 2mo ago
Last Modified Jun 17, 2026 2w ago
Description
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 Details
Base Score
Exploitability
Impact
Vector string
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N Attack Vector Network
Attack Complexity High
Privileges Required None
User Interaction None
Scope Unchanged
Confidentiality None
Integrity High
Availability None
Threat Intelligence
EPSS Exploit Probability
12.8% percentile
Exploit & Patch Status
Public Exploit Known
No Patch Available
Weaknesses 1
CWE-74
Affected Products 1
| Vendor | Product | Version | Range |
|---|---|---|---|
| jstedfast | mailkit | * | <4.16.0 |
References 1
- github.com https://github.com/jstedfast/MailKit/security/advisories/GHSA-9j88-vvj5-vhgr
Remediation
No remediation data recorded yet
Check vendor advisories and the NVD entry for patch availability.