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CVE-2025-49222

Mattermost Shared Channel Upload Type Validation Bypass

MEDIUM
6.8
CVSS Score
Published: August 21, 2025 at 07:59 AM UTC
Updated: June 17, 2026 at 09:30 AM UTC
2 products affected across 1 vendorMattermost ServerMattermost

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Severity
MEDIUM6.8
Exploit prediction
EPSS 0.3%
SSVC
No known exploit

Description

Mattermost versions 10.8.x <= 10.8.3, 10.5.x <= 10.5.8, 9.11.x <= 9.11.17, 10.9.x <= 10.9.2, 10.10.x <= 10.10.0 fail to validate upload types in remote cluster upload sessions which allows a system admin to upload non-attachment file types via shared channels that could potentially be placed in arbitrary filesystem directories.

Affected

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

Mattermost Server· Mattermost
95%
10.5.0 ≤ v < 10.5.910.8.0 ≤ v < 10.8.410.9.0 ≤ v < 10.9.39.11.0 ≤ v < 9.11.1810.10.0
Affected range stops below 10.5.9, so it looks safe — our inference, not a vendor statement
Affected range stops below 10.8.4, so it looks safe — our inference, not a vendor statement
Affected range stops below 10.9.3, so it looks safe — our inference, not a vendor statement
Affected range stops below 9.11.18, so it looks safe — our inference, not a vendor statement
Mattermost· Mattermost
60%
10.5.0 ≤ v ≤ 10.5.810.8.0 ≤ v ≤ 10.8.310.9.0 ≤ v ≤ 10.9.29.11.0 ≤ v ≤ 9.11.1710.10.010.5.010.8.010.9.09.11.0
Vendor states this is fixed in 10.10.1 (unaffected)
Vendor states this is fixed in 10.11.0 (unaffected)
Vendor states this is fixed in 10.5.9 (unaffected)
Vendor states this is fixed in 10.8.4 (unaffected)
Vendor states this is fixed in 10.9.3 (unaffected)
Vendor states this is fixed in 9.11.18 (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

6.8MEDIUMMattermost
Attack Vector
NETWORK
Complexity
LOW
Privileges
HIGH
User Interaction
NONE
Scope
CHANGED
Confidentiality
HIGH
Integrity
NONE
Availability
NONE
Vector?

Quick Info

StatusANALYZED
CWE
CWE-434

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