Mattermost CVE-2026-6346: Support Packets Leak Sensitive Credentials
The National Vulnerability Database has disclosed CVE-2026-6346, affecting Mattermost versions 11.5.x up to 11.5.1, 10.11.x up to 10.11.13, and 11.4.x up to 11.4.3. This vulnerability stems from Mattermost’s failure to properly sanitize sensitive configuration fields before generating support packets. The result is that these packets can contain plaintext credentials.
This flaw allows a Mattermost System Admin, or any party with access to a generated support packet, to extract highly sensitive information. The issue carries a CVSS score of 8.7 (HIGH), indicating a severe risk. It’s classified under CWE-200, highlighting the information exposure risk.
The attacker’s calculus here is straightforward: gain admin access, then exfiltrate a support packet. The impact is direct credential compromise, which can lead to further system access or lateral movement within an environment. Defenders need to recognize that even ‘trusted’ administrative functions can introduce significant risk if not meticulously secured.
What This Means For You
- If your organization uses Mattermost, you need to immediately identify all instances running affected versions. Patching to the latest secure versions is critical. Beyond patching, review your internal procedures for generating, storing, and accessing Mattermost support packets. Assume any past packets generated by affected versions contain plaintext secrets and rotate those credentials.
Related ATT&CK Techniques
🛡️ Detection Rules
2 rules · 6 SIEM formats2 detection rules auto-generated for this incident, mapped to MITRE ATT&CK. Sigma YAML is free — export to any SIEM format via the Intel Bot.
Data Exfiltration to Cloud Storage
title: Data Exfiltration to Cloud Storage
id: scw-2026-05-18-1
status: experimental
level: medium
description: |
Detects large file uploads to cloud storage services, which may indicate data exfiltration following the CVE-2026-6346 incident.
author: SCW Feed Engine (auto-generated)
date: 2026-05-18
references:
- https://shimiscyberworld.com/posts/nvd-CVE-2026-6346/
tags:
- attack.exfiltration
- attack.t1537
logsource:
category: proxy
detection:
selection:
dst_domain|contains:
- 'drive.google.com'
- 'dropbox.com'
- 'mega.nz'
- 'onedrive.live.com'
- 'anonfiles.com'
sc-bytes|gt: 5000000
condition: selection
falsepositives:
- Legitimate activity from CVE-2026-6346
Source: Shimi's Cyber World · License & reuse
Indicators of Compromise
| ID | Type | Indicator |
|---|---|---|
| CVE-2026-6346 | Information Disclosure | Mattermost versions 11.5.x <= 11.5.1 |
| CVE-2026-6346 | Information Disclosure | Mattermost versions 10.11.x <= 10.11.13 |
| CVE-2026-6346 | Information Disclosure | Mattermost versions 11.4.x <= 11.4.3 |
| CVE-2026-6346 | Information Disclosure | Sensitive configuration fields included in support packet generation |
| CVE-2026-6346 | Information Disclosure | Obtain sensitive credentials in plaintext via downloading a support packet from the System Console |
Written by SCW Vulnerability Desk
Source & Attribution
| Source Platform | NVD |
| Channel | National Vulnerability Database |
| Published | May 18, 2026 at 12:16 UTC |
This content was AI-rewritten and enriched by Shimi's Cyber World based on the original source. All intellectual property rights remain with the original author.
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