CVE-2026-6339 — Mattermost versions 11.5.x <= 11.5.1, 11.4.x <= 11.4.3 fail
CVE-2026-6339 — Mattermost versions 11.5.x <= 11.5.1, 11.4.x <= 11.4.3 fail to validate the X-Requested-With header on the burn-on-read reveal endpoint which allows an authenticated channel member to force the reveal of a burn-on-read message without recipient consent via a crafted Markdown image ta
What This Means For You
- If your environment is affected by CWE-346, review your exposure and prioritize patching based on your environment. Monitor vendor advisories for CVE-2026-6339 updates and patches.
Related ATT&CK Techniques
🛡️ Detection Rules
5 rules · 6 SIEM formats5 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.
Web Application Exploitation Attempt — CVE-2026-6339
title: Web Application Exploitation Attempt — CVE-2026-6339
id: scw-2026-05-18-1
status: experimental
level: high
description: |
Detects common exploitation patterns targeting web applications. Review CVE-2026-6339 advisories for specific indicators.
author: SCW Feed Engine (auto-generated)
date: 2026-05-18
references:
- https://shimiscyberworld.com/posts/nvd-CVE-2026-6339/
tags:
- attack.initial_access
- attack.t1190
logsource:
category: webserver
detection:
selection:
cs-uri-query|contains:
- '..'
- 'SELECT'
- 'UNION'
- '<script'
- 'cmd='
- '/etc/passwd'
condition: selection
falsepositives:
- Legitimate activity from CVE-2026-6339
Source: Shimi's Cyber World · License & reuse
Indicators of Compromise
| ID | Type | Indicator |
|---|---|---|
| CVE-2026-6339 | vulnerability | CVE-2026-6339 |
| CWE-346 | weakness | CWE-346 |
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 curated and summarized by Shimi's Cyber World for informational purposes. It is not copied or republished in full. All intellectual property rights remain with the original author and source.
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