CVE-2026-2476: Mattermost Plugins Info Disclosure Flaw

CVE-2026-2476 Overview

CVE-2026-2476 is an Information Disclosure vulnerability affecting Mattermost Plugins versions <=2.0.3.0. The vulnerability arises from improper masking of sensitive configuration values, allowing attackers with access to support packets to obtain original plugin settings via exported configuration data. This weakness is classified as CWE-200 (Exposure of Sensitive Information to an Unauthorized Actor).

Critical Impact
Attackers with access to support packets can extract sensitive plugin configuration data, potentially exposing credentials, API keys, and other secrets that should remain protected.

Affected Products

Mattermost Plugins versions <=2.0.3.0

Discovery Timeline

2026-03-16 - CVE CVE-2026-2476 published to NVD
2026-03-16 - Last updated in NVD database

Technical Details for CVE-2026-2476

Vulnerability Analysis

This vulnerability represents an Information Disclosure flaw in Mattermost Plugins where sensitive configuration values are not properly masked during the support packet export process. When administrators generate support packets for troubleshooting purposes, these packages contain configuration data that should have sensitive fields redacted or obfuscated. Due to the improper implementation of the masking functionality, certain plugin settings containing sensitive information are exported in their original, unmasked form.

The vulnerability requires the attacker to have access to support packets, which typically contain diagnostic information intended for support personnel. While this access requirement limits the attack surface, the exposure of sensitive configuration data could lead to credential theft, unauthorized access to connected services, or further compromise of the Mattermost deployment.

Root Cause

The root cause is improper implementation of data masking functionality within the Mattermost Plugins configuration export mechanism. The system fails to properly identify and mask all sensitive configuration fields before including them in support packet exports, violating the principle of data minimization and secure data handling.

Attack Vector

The attack vector is network-based and requires the attacker to have privileged access to obtain support packets. The attack scenario involves:

An attacker gains access to support packets, either through compromised administrative access, insider threat, or interception of support communications
The attacker analyzes the exported configuration data within the support packet
Sensitive plugin settings that should be masked are found in their original form
The attacker extracts credentials, API keys, or other sensitive configuration values
These extracted secrets can then be used for lateral movement or accessing connected services

The vulnerability exploits the trust placed in the support packet generation process, where administrators expect sensitive data to be properly redacted.

Detection Methods for CVE-2026-2476

Indicators of Compromise

Unusual access patterns to support packet generation functionality
Unauthorized download or export of support diagnostic packages
Evidence of support packets being transmitted to unauthorized recipients
Unexpected access to Mattermost plugin configuration endpoints

Detection Strategies

Monitor administrative actions related to support packet generation and export
Implement alerting on support packet downloads by non-authorized personnel
Audit access logs for the Mattermost administrative console
Review outbound network traffic for support packet data exfiltration

Monitoring Recommendations

Enable detailed logging for all administrative actions within Mattermost
Configure alerts for support packet generation events
Monitor for access to configuration export endpoints
Implement file integrity monitoring on support packet storage locations

How to Mitigate CVE-2026-2476

Immediate Actions Required

Upgrade Mattermost Plugins to a version newer than 2.0.3.0
Audit previously generated support packets for sensitive data exposure
Rotate any credentials or API keys that may have been exposed in support packets
Restrict access to support packet generation to essential personnel only
Review and limit distribution of previously shared support packets

Patch Information

Mattermost has addressed this vulnerability in versions newer than 2.0.3.0. Organizations should update their Mattermost Plugins installation to the latest available version. For detailed patch information and security updates, refer to the Mattermost Security Updates page. The advisory is tracked as MMSA-2026-00606.

Workarounds

Manually redact sensitive information from support packets before sharing with third parties
Implement strict access controls limiting who can generate and access support packets
Avoid generating support packets until the patch can be applied
If support packets must be generated, review their contents for sensitive data before distribution
Consider using network segmentation to limit access to administrative functions