CVE-2017-18911Network attack vector

SMTP traffic interception via skipped certificate validation

Published Jun 19, 2020 · Updated Aug 5, 2024

Improper certificate validation in Mattermost Server before 3.8.2, 3.7.5, and 3.6.7 allows attackers to read and alter SMTP traffic. The SMTP TLS client allows X.509 verification to be skipped rather than rejecting an unauthenticated mail-server certificate. Exploitation requires a TLS-based email configuration and a network position from which a substitute mail-server certificate can be presented.

CVSS severity9.1
Critical
EPSS probability0.66%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper certificate validation in Mattermost Server before 3.8.2, 3.7.5, and 3.6.7 allows attackers to read and alter SMTP traffic. The SMTP TLS client allows X.509 verification to be skipped rather than rejecting an unauthenticated mail-server certificate. Exploitation requires a TLS-based email configuration and a network position from which a substitute mail-server certificate can be presented.

The record

CVE
CVE-2017-18911
Published
Jun 19, 2020
Updated
Aug 5, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-295, T1557
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 19, 2020CVE publishedPublication date reported by the CVE source.
  2. Aug 5, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

9.1GitHub Advisory DatabaseCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-295Improper Certificate Validation
T1557Adversary-in-the-Middle

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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