Mattermost up to 11.6.x Websocket Connection information disclosure

Summaryinfo

A vulnerability identified as problematic has been detected in Mattermost up to 10.11.15/10.11.16/11.5.4/11.6.1/11.6.x. Affected by this vulnerability is an unknown functionality of the component Websocket Connection Handler. This manipulation causes information disclosure. This vulnerability is registered as CVE-2026-3433. Remote exploitation of the attack is possible. No exploit is available. You should upgrade the affected component.

Detailsinfo

A vulnerability was found in Mattermost up to 10.11.15/10.11.16/11.5.4/11.6.1/11.6.x. It has been declared as problematic. Affected by this vulnerability is some unknown functionality of the component Websocket Connection Handler. The manipulation with an unknown input leads to a information disclosure vulnerability. The CWE definition for the vulnerability is CWE-200. The product exposes sensitive information to an actor that is not explicitly authorized to have access to that information. As an impact it is known to affect confidentiality. The summary by CVE is:

Mattermost versions 11.6.x <= 11.6.1, 11.5.x <= 11.5.4, 10.11.x <= 10.11.15, 10.11.x <= 10.11.16 fail to restrict role_updated websocket event broadcasts to members of the affected team or channel which allows an authenticated attacker with guest-level access to observe permission scheme change notifications for private teams they are not a member of via the websocket connection.. Mattermost Advisory ID: MMSA-2026-00616

The weakness was published by 0x7oda7123. The advisory is shared at mattermost.com. This vulnerability is known as CVE-2026-3433 since 03/02/2026. The exploitation appears to be easy. The attack can be launched remotely. Neither technical details nor an exploit are publicly available. MITRE ATT&CK project uses the attack technique T1592 for this issue.

Upgrading to version 10.11.16, 10.11.17, 11.5.5, 11.6.2 or 11.7.0 eliminates this vulnerability.

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Productinfo

Type

• Groupware Software

Name

• Mattermost

Version

• 10.11.0
• 10.11.1
• 10.11.2
• 10.11.3
• 10.11.4
• 10.11.5
• 10.11.6
• 10.11.7
• 10.11.8
• 10.11.9
• 10.11.10
• 10.11.11
• 10.11.12
• 10.11.13
• 10.11.14
• 10.11.15
• 10.11.16
• 11.0
• 11.1
• 11.2
• 11.3
• 11.4
• 11.5
• 11.5.0
• 11.5.1
• 11.5.2
• 11.5.3
• 11.5.4
• 11.6
• 11.6.0
• 11.6.1

License

• open-source

CPE 2.3info

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CPE 2.2info

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