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NVD Vulnerability Details :
CVE-2026-27656
Analyzed
More InfoOfficial Page
Source-responsibledisclosure@mattermost.com
View Known Exploited Vulnerability (KEV) details
Published At-25 Mar, 2026 | 17:16
Updated At-26 Mar, 2026 | 18:51

Mattermost versions 11.4.x <= 11.4.0, 11.3.x <= 11.3.1, 11.2.x <= 11.2.3, 10.11.x <= 10.11.11 fail to properly validate user identity in the OpenID {{IsSameUser()}} comparison logic, which allows an attacker to take over arbitrary user accounts via an overly permissive substring matching flaw in the user discovery flow.. Mattermost Advisory ID: MMSA-2026-00590

CISA Catalog
Date AddedDue DateVulnerability NameRequired Action
N/A
Date Added: N/A
Due Date: N/A
Vulnerability Name: N/A
Required Action: N/A
Metrics
TypeVersionBase scoreBase severityVector
Secondary3.15.7MEDIUM
CVSS:3.1/AV:N/AC:H/PR:H/UI:R/S:U/C:H/I:H/A:N
Primary3.16.1MEDIUM
CVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:U/C:H/I:H/A:N
Type: Secondary
Version: 3.1
Base score: 5.7
Base severity: MEDIUM
Vector:
CVSS:3.1/AV:N/AC:H/PR:H/UI:R/S:U/C:H/I:H/A:N
Type: Primary
Version: 3.1
Base score: 6.1
Base severity: MEDIUM
Vector:
CVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:U/C:H/I:H/A:N
CPE Matches
Mattermost, Inc.
mattermost
>>mattermost_server>>Versions from 10.11.0(inclusive) to 10.11.12(exclusive)
cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*
Mattermost, Inc.
mattermost
>>mattermost_server>>Versions from 11.2.0(inclusive) to 11.2.4(exclusive)
cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*
Mattermost, Inc.
mattermost
>>mattermost_server>>Versions from 11.3.0(inclusive) to 11.3.2(exclusive)
cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*
Mattermost, Inc.
mattermost
>>mattermost_server>>Versions from 11.4.0(inclusive) to 11.4.1(exclusive)
cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*
Weaknesses
CWE IDTypeSource
CWE-303Secondaryresponsibledisclosure@mattermost.com
CWE ID: CWE-303
Type: Secondary
Source: responsibledisclosure@mattermost.com
Evaluator Description
Evaluator Impact

Evaluator Solution

Vendor Statements
References
HyperlinkSourceResource
https://mattermost.com/security-updatesresponsibledisclosure@mattermost.com
Vendor Advisory
Hyperlink: https://mattermost.com/security-updates
Source: responsibledisclosure@mattermost.com
Resource:
Vendor Advisory
Change History
0Changes found
Details not found