CVE-2026-3524

High

Published: 06 April 2026

Published

06 April 2026

Modified

07 April 2026

KEV Added

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Patch

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CVSS Score 8.8 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

EPSS Score 0.0002 5.1th percentile

Risk Priority 18 60% EPSS · 20% KEV · 20% CVSS

Summary

CVE-2026-3524 is a high-severity Missing Authorization (CWE-862) vulnerability in Mattermost Plugin Legal Hold (inferred from references). Its CVSS base score is 8.8 (High).

Operationally, exploitation aligns with the MITRE ATT&CK technique Data from Information Repositories (T1213); ranked at the 5.1th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.

The strongest mitigations our analysis identified are NIST 800-53 AC-3 (Access Enforcement) and SI-2 (Flaw Remediation).

Threat & Defense at a Glance

What attackers do: exploitation maps to Data from Information Repositories (T1213) and 3 other techniques. What defenders deploy: see the NIST 800-53 controls recommended below.

Threat & Defense Details

Mitigating Controls (NIST 800-53 r5)AI

AC-3 Access Enforcement good match

prevent

Enforces approved authorizations for logical access to information and system resources, directly mitigating the failure to halt request processing after a failed authorization check in the plugin's ServeHTTP function.

SI-2 Flaw Remediation good match

prevent

Requires timely identification, reporting, and correction of system flaws, such as patching Mattermost Legal Hold plugin versions <=1.1.4 to remediate the authorization vulnerability.

AC-6 Least Privilege partial match

prevent

Employs least privilege to restrict authorized accesses necessary for tasks, limiting damage from low-privilege authenticated attackers exploiting the authorization bypass.

MITRE ATT&CK Enterprise TechniquesAI

T1213 Data from Information Repositories Collection

Adversaries may leverage information repositories to mine valuable information.

attack.mitre.org →

T1485 Data Destruction Impact

Adversaries may destroy data and files on specific systems or in large numbers on a network to interrupt availability to systems, services, and network resources.

attack.mitre.org →

T1565 Data Manipulation Impact

Adversaries may insert, delete, or manipulate data in order to influence external outcomes or hide activity, thus threatening the integrity of the data.

attack.mitre.org →

T1567 Exfiltration Over Web Service Exfiltration

Adversaries may use an existing, legitimate external Web service to exfiltrate data rather than their primary command and control channel.

attack.mitre.org →

Why these techniques?

Missing authorization in plugin API enables low-priv authenticated attackers to access (T1213 Data from Information Repositories), download/exfil (T1567 Exfiltration Over Web Service), create/manipulate (T1565 Data Manipulation), and delete (T1485 Data Destruction) legal hold data.

Confidence: HIGH · MITRE ATT&CK Enterprise v18.1

NVD Description

Mattermost Plugin Legal Hold versions <=1.1.4 fail to halt request processing after a failed authorization check in ServeHTTP which allows an authenticated attacker to access, create, download, and delete legal hold data via crafted API requests to the plugin's endpoints.…

Mattermost Advisory ID: MMSA-2026-00621

Deeper analysisAI

CVE-2026-3524 is a missing authorization vulnerability (CWE-862) in the Mattermost Plugin Legal Hold versions <=1.1.4. The flaw occurs in the ServeHTTP function, where request processing continues even after a failed authorization check. This enables unauthorized operations on legal hold data through the plugin's API endpoints. The vulnerability carries a CVSS v3.1 base score of 8.8 (AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H) and was published on 2026-04-06.

An authenticated attacker with low privileges (PR:L) can exploit this vulnerability remotely over the network (AV:N) with low complexity (AC:L) and no user interaction (UI:N). By crafting API requests to the plugin's endpoints, the attacker can access, create, download, and delete legal hold data, achieving high confidentiality, integrity, and availability impacts (C:H/I:H/A:H) within the unchanged security scope (S:U).

Mattermost Advisory ID MMSA-2026-00621 addresses this issue. Further details on mitigation and patches are available in the security updates at https://mattermost.com/security-updates.