CVE-2024-39839Network attack vector

Unauthorized username changes via unchecked remote synchronization

Published Aug 1, 2024 · Updated Aug 1, 2024

Improper access control in Mattermost shared channels allows remote authenticated users to alter a username synchronized to another server. The shared-channel user synchronization path accepts an arbitrary remote_username property from a remote user and stores it locally without rejecting self-assignment. Shared channels must be enabled, and the account must not have been synchronized previously; the consequence is an unauthorized integrity change to the displayed remote identity.

CVSS severity4.3
Medium
EPSS probability0.34%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper access control in Mattermost shared channels allows remote authenticated users to alter a username synchronized to another server. The shared-channel user synchronization path accepts an arbitrary remote_username property from a remote user and stores it locally without rejecting self-assignment. Shared channels must be enabled, and the account must not have been synchronized previously; the consequence is an unauthorized integrity change to the displayed remote identity.

The record

CVE
CVE-2024-39839
Published
Aug 1, 2024
Updated
Aug 1, 2024
Vendor
Mattermost
Product
Mattermost
Classifications
CWE-284, T1036
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Aug 1, 2024CVE publishedPublication date reported by the CVE source.
  2. Aug 1, 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?

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

  1. Affected versionversion=9.5.0 <=9.5.6
  2. Affected versionversion=9.7.0 <=9.7.5
  3. Affected versionversion=9.8.0 <=9.8.1
  4. Affected versionversion=9.9.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Mattermost · Mattermostversion=9.5.0 <=9.5.6; version=9.7.0 <=9.7.5; version=9.8.0 <=9.8.1; version=9.9.0

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
4.3NIST NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N
5.3GitHubCVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA: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 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-284Improper Access Control
T1036Masquerading

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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