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CVE-2017-18911

29
FAUCET Score

CVE-2017-18911 describes a critical vulnerability in Mattermost Server versions before 3.8.2, 3.7.5, and 3.6.7, where X.509 certificate validation for TLS-based email servers can be bypassed. This flaw carries a CVSS score of 9.1 (CRITICAL), indicating a network-based attack with low complexity that could lead to complete compromise of confidentiality and integrity without user interaction. While there is no known active exploitation, public exploit code, or KEV listing, the vulnerability has garnered significant community discussion with 11 mentions, suggesting awareness and potential for future exploitation.

Impacted Technologies

VendorProductVersion(s)CPE
< 3.6.7CPE matchmatch criteria
cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*
>= 3.7.0, < 3.7.5CPE matchmatch criteria
cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*
>= 3.8.0, < 3.8.2CPE matchmatch criteria
cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.1

9.1CRITICAL

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
HIGH
Integrity Impact
HIGH
Availability Impact
NONE
Exploitability Score
3.9
Impact Score
5.2
CvssVersion
3.1

Exploit Intelligence

EPSS Score
0.67%
Probability of exploitation in next 30 days
EPSS Percentile
48.3%
Percentile rank of EPSS score among Peer Group
As of 2026-07-28
Model: v2026.06.15
This CVE's current EPSS score of 0.0067 is in the 30th percentile among its peer group of 36,897 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.1 Reddit, 0.3 Bluesky, 0.3 Mastodon, and 2.4 GitHub mentions.

Media Mentions

The average CVE in this peer group has 0.3 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Patch Available

Vendor Patches (3)

gopatch availablevia ghsa
Product: github.com/mattermost/mattermost-serverFixed in: 3.6.7-rc1
gopatch availablevia ghsa
Product: github.com/mattermost/mattermost-serverFixed in: 3.7.5
gopatch availablevia ghsa
Product: github.com/mattermost/mattermost-serverFixed in: 3.8.2

Vendor Advisories (1)

goGHSA-m462-mqw4-2c8mcritical

Mattermost Server has X.509 Improper Certificate Validation

May 24, 2022

References

mattermost.com / security-updates
Vendor Advisory