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CVE-2019-20866

19
FAUCET Score

CVE-2019-20866 is a medium-severity vulnerability affecting Mattermost Server versions prior to 5.12.0. It stems from the mishandling of IP address information when a Proxy HTTP header is used instead of the IP packet's source address. This flaw could lead to information disclosure (CVSS 5.3, C:L), potentially revealing sensitive network details. There is currently no evidence of active exploitation, publicly available exploit code, or significant community discussion surrounding this CVE.

Impacted Technologies

VendorProductVersion(s)CPE
< 5.12.0CPE matchmatch criteria
cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.1

5.3MEDIUM

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

Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
LOW
Integrity Impact
NONE
Availability Impact
NONE
Exploitability Score
3.9
Impact Score
1.4
CvssVersion
3.1

Exploit Intelligence

EPSS Score
0.92%
Probability of exploitation in next 30 days
EPSS Percentile
56.6%
Percentile rank of EPSS score among Peer Group
As of 2026-07-28
Model: v2026.06.15
This CVE's current EPSS score of 0.0092 is in the 35th percentile among its peer group of 23,725 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.0 Reddit, 0.1 Bluesky, 0.0 Mastodon, and 0.4 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

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

Remediation

Remediation records are not available for this CVE.

References

mattermost.com / security-updates
Vendor Advisory