How severe is CVE-2024-39839?

CVE-2024-39839 has a CVSS 3.x base score of 4.3, rated medium severity. It is exploitable over network with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is none, integrity low, and availability none.

Is CVE-2024-39839 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (26th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2024-39839?

CVE-2024-39839 primarily affects Mattermost Mattermost Server. In total, 2 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2024-39839?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

Does CVE-2024-39839 have an EU (EUVD) identifier?

Yes. CVE-2024-39839 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2024-2663.

When was CVE-2024-39839 published?

CVE-2024-39839 was published on 2024-08-01 and last updated on 2026-06-17.

CVE-2024-39839

CVE-2024-39839 is a medium-severity vulnerability in Mattermost Mattermost Server with a CVSS 3.x base score of 4.3. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-284.

Key facts

Severity: Medium (CVSS 3.x base score 4.3)
EPSS exploit prediction: 0% (26th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2024-2663
Weakness: CWE-284
Affected product: Mattermost Mattermost Server
Published: 2024-08-01
Last modified: 2026-06-17

Description

Mattermost versions 9.9.x <= 9.9.0, 9.5.x <= 9.5.6, 9.7.x <= 9.7.5, 9.8.x <= 9.8.1 fail to disallow users to set their own remote username, when shared channels were enabled, which allows a user on a remote to set their remote username prop to an arbitrary string, which would be then synced to the local server as long as the user hadn't been synced before.

Frequently asked questions

What is CVE-2024-39839?: Mattermost versions 9.9.x <= 9.9.0, 9.5.x <= 9.5.6, 9.7.x <= 9.7.5, 9.8.x <= 9.8.1 fail to disallow users to set their own remote username, when shared channels were enabled, which allows a user on a remote to set their remote username prop to an arbitrary string, which would be then synced to the local server as long as the user hadn't been synced before.
How severe is CVE-2024-39839?: CVE-2024-39839 has a CVSS 3.x base score of 4.3, rated medium severity. It is exploitable over network with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is none, integrity low, and availability none.
Is CVE-2024-39839 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (26th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2024-39839?: CVE-2024-39839 primarily affects Mattermost Mattermost Server. In total, 2 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2024-39839?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2024-39839 have an EU (EUVD) identifier?: Yes. CVE-2024-39839 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2024-2663.
When was CVE-2024-39839 published?: CVE-2024-39839 was published on 2024-08-01 and last updated on 2026-06-17.

References

https://mattermost.com/security-updates

Affected products (2)

cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*
cpe:2.3:a:mattermost:mattermost_server:9.9.0:*:*:*:*:*:*:*

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