CVE-2023-2808Network attack vector

Blocked-domain link previews via UTF confusable URLs

Published May 29, 2023 · Updated Dec 6, 2024

Improper input validation in Mattermost release lines before 7.1.9, 7.8.4, and 7.9.3 allows remote authenticated users to preview blocked domains. Mattermost compares a link host with preview restrictions without first normalizing UTF confusable characters, so a crafted hostname bypasses the domain check. Posting the link requires an authenticated account and causes the server to fetch and render a preview from a domain that policy intended to exclude.

CVSS severity4.3
Medium
EPSS probability0.41%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper input validation in Mattermost release lines before 7.1.9, 7.8.4, and 7.9.3 allows remote authenticated users to preview blocked domains. Mattermost compares a link host with preview restrictions without first normalizing UTF confusable characters, so a crafted hostname bypasses the domain check. Posting the link requires an authenticated account and causes the server to fetch and render a preview from a domain that policy intended to exclude.

The record

CVE
CVE-2023-2808
Published
May 29, 2023
Updated
Dec 6, 2024
Vendor
Mattermost
Product
Mattermost
Classifications
CWE-20
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. May 29, 2023CVE publishedPublication date reported by the CVE source.
  2. Dec 6, 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?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0 <7.1.9
  2. Affected versionversion=0 <7.8.4
  3. Affected versionversion=0 <7.9.3

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Mattermost · Mattermostversion=0 <7.1.9; version=0 <7.8.4; version=0 <7.9.3

Published CVSS scores

4.3Mattermost, Inc.CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N
5.3NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/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

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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