Mattermost up to 10.11.21/11.7.6/11.8.3 channelId permission

CVSS Meta Temp Score
CVSS is a standardized scoring system to determine possibilities of attacks. The Temp Score considers temporal factors like disclosure, exploit and countermeasures. The unique Meta Score calculates the average score of different sources to provide a normalized scoring system.
Current Exploit Price (≈)
Our analysts are monitoring exploit markets and are in contact with vulnerability brokers. The range indicates the observed or calculated exploit price to be seen on exploit markets. A good indicator to understand the monetary effort required for and the popularity of an attack.
CTI Interest Score
Our Cyber Threat Intelligence team is monitoring different web sites, mailing lists, exploit markets and social media networks. The CTI Interest Score identifies the interest of attackers and the security community for this specific vulnerability in real-time. A high score indicates an elevated risk to be targeted for this vulnerability.
5.3$0-$5k3.38

Summaryinfo

A vulnerability marked as problematic has been reported in Mattermost up to 10.11.21/11.7.6/11.8.3. The affected element is an unknown function. This manipulation of the argument channelId causes permission. This vulnerability is tracked as CVE-2026-9859. The attack is possible to be carried out remotely. No exploit exists.

Detailsinfo

A vulnerability was found in Mattermost up to 10.11.21/11.7.6/11.8.3. It has been declared as problematic. Affected by this vulnerability is an unknown code. The manipulation of the argument channelId with an unknown input leads to a permission vulnerability. The CWE definition for the vulnerability is CWE-275. As an impact it is known to affect confidentiality. The summary by CVE is:

Mattermost versions 11.7.x <= 11.7.6, 10.11.x <= 10.11.21, 11.8.x <= 11.8.3 fail to enforce PermissionManageBoardRoles on the channelId field of the batch endpoint, which allows an authenticated board editor to relink any board they can edit to an arbitrary channel via a crafted PATCH request. Mattermost Advisory ID: MMSA-2026-00686

It is possible to read the advisory at mattermost.com. This vulnerability is known as CVE-2026-9859 since 05/28/2026. The exploitation appears to be easy. The attack can be launched remotely. Technical details of the vulnerability are known, but there is no available exploit. The attack technique deployed by this issue is T1222 according to MITRE ATT&CK.

Upgrading to version 10.11.22, 11.7.7, 11.8.4 or 11.9.0 eliminates this vulnerability.

The vulnerability is also documented in the vulnerability database at EUVD (EUVD-2026-60541). Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

Productinfo

Type

Name

Version

License

CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 5.4
VulDB Meta Temp Score: 5.3

VulDB Base Score: 4.3
VulDB Temp Score: 4.1
VulDB Vector: 🔒
VulDB Reliability: 🔍

CNA Base Score: 6.5
CNA Vector (Mattermost): 🔒

CVSSv2info

AVACAuCIA
💳💳💳💳💳💳
💳💳💳💳💳💳
💳💳💳💳💳💳
VectorComplexityAuthenticationConfidentialityIntegrityAvailability
UnlockUnlockUnlockUnlockUnlockUnlock
UnlockUnlockUnlockUnlockUnlockUnlock
UnlockUnlockUnlockUnlockUnlockUnlock

VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Permission
CWE: CWE-275 / CWE-266
CAPEC: 🔒
ATT&CK: 🔒

Physical: No
Local: No
Remote: Yes

Availability: 🔒
Status: Not defined
Price Prediction: 🔍
Current Price Estimation: 🔒

0-DayUnlockUnlockUnlockUnlock
TodayUnlockUnlockUnlockUnlock

Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔒

Upgrade: Mattermost 10.11.22/11.7.7/11.8.4/11.9.0

Timelineinfo

05/28/2026 CVE reserved
08/17/2026 +81 days VulDB entry created
08/18/2026 +0 days Advisory disclosed
08/18/2026 +0 days VulDB entry last update

Sourcesinfo

Advisory: mattermost.com
Status: Confirmed

CVE: CVE-2026-9859 (🔒)
GCVE (CVE): GCVE-0-2026-9859
GCVE (VulDB): GCVE-100-391507
EUVD: 🔒

Entryinfo

Created: 08/18/2026 00:27
Updated: 08/18/2026 02:12
Changes: 08/18/2026 00:27 (63), 08/18/2026 02:12 (1)
Complete: 🔍
Cache ID: 216::103

Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

Discussion

No comments yet. Languages: en.

Please log in to comment.

◂ PreviousOverviewNext ▸

Do you want to use VulDB in your project?

Use the official API to access entries easily!