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CVE-2026-82920

Mattermost ABAC parent policy bypass via policy update endpoint

MEDIUM
5.5
CVSS Score
Published: September 14, 2026 at 01:59 PM UTC
Updated: October 7, 2026 at 06:04 PM UTC
2 products affected across 1 vendorMattermost ServerMattermost

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Severity
MEDIUM5.5
Exploit prediction
EPSS 0.3%
SSVC
No known exploit

Description

Mattermost versions 11.9.x <= 11.9.0, 11.8.x <= 11.8.4, 11.7.x <= 11.7.7 fail to enforce authorization boundaries on the access control policy update endpoint which allows a channel or team administrator to detach a system-assigned ABAC parent policy via a crafted PUT /api/v4/access_control_policies request with an empty imports list.. Mattermost Advisory ID: MMSA-2026-00724

Affected

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

Mattermost Server· Mattermost
95%
11.7.0 ≤ v < 11.7.811.8.0 ≤ v < 11.8.511.9.0 ≤ v < 11.9.1
Affected range stops below 11.7.8, so it looks safe — our inference, not a vendor statement
Affected range stops below 11.8.5, so it looks safe — our inference, not a vendor statement
Affected range stops below 11.9.1, so it looks safe — our inference, not a vendor statement
Mattermost· Mattermost
60%
11.7.0 ≤ v ≤ 11.7.711.8.0 ≤ v ≤ 11.8.411.7.011.8.011.9.0
Vendor states this is fixed in 11.10.0 (unaffected)
Vendor states this is fixed in 11.7.8 (unaffected)
Vendor states this is fixed in 11.8.5 (unaffected)
Vendor states this is fixed in 11.9.1 (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: cverecord
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

5.5MEDIUMMattermost
Attack Vector
NETWORK
Complexity
LOW
Privileges
HIGH
User Interaction
NONE
Scope
CHANGED
Confidentiality
LOW
Integrity
LOW
Availability
NONE
Vector?

Quick Info

StatusANALYZED
CWE
CWE-863

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