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NVD 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.
Priority
LOW
Exploitation
NONE
PoC
YES
Patch
NONE
Momentum
NONE
If you run products in this scope, you should treat this CVE as relevant to your environment.
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-M… https://www.cve.org/CVERecord?id=CVE-2026-41319
Post summary
The text announces CVE-2026-41319, a STARTTLS response injection flaw in MailKit before v4.16.0, presenting basic technical details without evidence of exploitation or mitigation.
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| Part | Vendor | Product | Version | Target SW | Target HW |
|---|---|---|---|---|---|
| App | jstedfast | mailkit | - | - | - |