How severe is CVE-2026-41319?

CVE-2026-41319 has a CVSS 3.x base score of 6.5, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is none, integrity high, and availability none.

Is CVE-2026-41319 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (13th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-41319?

CVE-2026-41319 affects Jstedfast Mailkit. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-41319?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

Does CVE-2026-41319 have an EU (EUVD) identifier?

Yes. CVE-2026-41319 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-25388.

When was CVE-2026-41319 published?

CVE-2026-41319 was published on 2026-04-24 and last updated on 2026-06-17.

CVE-2026-41319

CVE-2026-41319 is a medium-severity vulnerability in Jstedfast Mailkit with a CVSS 3.x base score of 6.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-74.

Key facts

Severity: Medium (CVSS 3.x base score 6.5)
EPSS exploit prediction: 0% (13th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-25388
Weakness: CWE-74
Affected product: Jstedfast Mailkit
Published: 2026-04-24
Last modified: 2026-06-17

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.

Frequently asked questions

What is 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.
How severe is CVE-2026-41319?: CVE-2026-41319 has a CVSS 3.x base score of 6.5, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is none, integrity high, and availability none.
Is CVE-2026-41319 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (13th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-41319?: CVE-2026-41319 affects Jstedfast Mailkit. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-41319?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2026-41319 have an EU (EUVD) identifier?: Yes. CVE-2026-41319 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-25388.
When was CVE-2026-41319 published?: CVE-2026-41319 was published on 2026-04-24 and last updated on 2026-06-17.

References

https://github.com/jstedfast/MailKit/security/advisories/GHSA-9j88-vvj5-vhgr

Affected products (1)

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

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