CVE-2026-41319
MEDIUM
MEDIUM
Priority: 0.01
BB Relevance:
62/100
Published: 2026-04-24
Modified: 2026-10-26
First seen: 2026-10-29
Status: active
Attack Surface
Network
No Auth
No Interaction
Integ. Impact
CVSS Vector Breakdown
AV:
Network
AC:
High
PR:
None
UI:
None
S:
Unchanged
C:
None
I:
High
A:
None
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.
Weakness Classification (1)
References & Advisories (1)
Exploit
Vendor Advisory