EUVD-2026-16234
GHSA-3439-vqgj-2gcf
CVSS Vector
CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:C/C:H/I:H/A:H
Lifecycle Timeline
4Description
Mattermost versions 11.2.x <= 11.2.2, 10.11.x <= 10.11.10, 11.4.x <= 11.4.0, 11.3.x <= 11.3.1 fail to sanitize user-controlled post content in the mmctl commands terminal output which allows attackers to manipulate administrator terminals via crafted messages containing ANSI and OSC escape sequences that enable screen manipulation, fake prompts, and clipboard hijacking.. Mattermost Advisory ID: MMSA-2026-00599
Analysis
Mattermost's mmctl command-line administration tool fails to sanitize ANSI and OSC escape sequences embedded in user-generated post content, enabling authenticated low-privilege attackers to inject malicious terminal control codes when administrators export or query messages. Exploitation allows screen manipulation, fake prompt injection, and clipboard hijacking against administrators running mmctl commands, potentially leading to secondary code execution if administrators are tricked into running injected commands. …
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Remediation
Within 24 hours: Identify all administrators with mmctl access and restrict command-line message export/query operations to isolated terminals without external access. Within 7 days: Document all mmctl usage and implement mandatory terminal safety training for administrators emphasizing verification of command sources before execution. …
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Priority Score
Vendor Status
Debian
Bug #823556| Release | Status | Fixed Version | Urgency |
|---|---|---|---|
| open | - | - |
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External POC / Exploit Code
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