CVE-2017-18889Network attack vector

Authenticated system-post spoofing via integration APIs

Published Jun 19, 2020 · Updated Aug 5, 2024

Improper input validation in Mattermost Server before 4.3.0, 4.2.1, and 4.1.2 allows remote authenticated users to forge system posts. The flaw lies in v3 and v4 REST API handling of webhook and slash-command posts, but Mattermost has not published the omitted validation or affected code locus. The attack requires low-privileged network access and can misrepresent trusted system activity without reading data or interrupting service.

CVSS severity4.3
Medium
EPSS probability0.66%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Improper input validation in Mattermost Server before 4.3.0, 4.2.1, and 4.1.2 allows remote authenticated users to forge system posts. The flaw lies in v3 and v4 REST API handling of webhook and slash-command posts, but Mattermost has not published the omitted validation or affected code locus. The attack requires low-privileged network access and can misrepresent trusted system activity without reading data or interrupting service.

The record

CVE
CVE-2017-18889
Published
Jun 19, 2020
Updated
Aug 5, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-20, T1565.001
Attack vector
network
Privileges
authenticated

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

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

4.0NIST NVDAV:N/AC:L/Au:S/C:N/I:P/A:N
4.3NIST NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N
4.3GitHub Advisory DatabaseCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-20Improper Input Validation
T1565.001Stored Data Manipulation

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

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo