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CVE-2024-39839

Remote username set to an arbitrary string by remote user

MEDIUM
4.3
CVSS Score
Published: August 1, 2024 at 02:05 PM UTC
Updated: June 17, 2026 at 07:42 AM UTC
2 products affected across 1 vendorMattermost ServerMattermost

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Severity
MEDIUM4.3
Exploit prediction
EPSS 0.3%
SSVC
No known exploit

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.

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

Mattermost Server· Mattermost
95%
9.5.0 ≤ v < 9.5.79.7.0 ≤ v < 9.7.69.8.0 ≤ v < 9.8.29.9.0
Affected range stops below 9.5.7, so it looks safe — our inference, not a vendor statement
Affected range stops below 9.7.6, so it looks safe — our inference, not a vendor statement
Affected range stops below 9.8.2, so it looks safe — our inference, not a vendor statement
Mattermost· Mattermost
60%
9.5.0 ≤ v ≤ 9.5.69.7.0 ≤ v ≤ 9.7.59.8.0 ≤ v ≤ 9.8.19.5.09.7.09.8.09.9.0
Vendor states this is fixed in 9.10.0 (unaffected)
Vendor states this is fixed in 9.5.7 (unaffected)
Vendor states this is fixed in 9.7.6 (unaffected)
Vendor states this is fixed in 9.8.2 (unaffected)
Vendor states this is fixed in 9.9.1 (unaffected)

Remediation

No guide yet

No remediation guidance has been written for this CVE yet. What the record does show:

Patch and advisory references

References (1)

Vendor Advisory
Source: [email protected]
https://mattermost.com/security-updates

SSVC — Action Prioritization

SSVCNo known exploitNot automatablePartial impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

4.3MEDIUMMattermost
Attack Vector
NETWORK
Complexity
LOW
Privileges
LOW
User Interaction
NONE
Scope
UNCHANGED
Confidentiality
NONE
Integrity
LOW
Availability
NONE
Vector?

Quick Info

StatusANALYZED
CWE
CWE-284NVD-CWE-noinfo

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