CVE-2026-9708

Incoming webhook user attribution via unvalidated webhook owner

Published Jul 13, 2026 CVSS 3.1 · 4.9 Medium EPSS < 1% KEV · Not listed

Description

Mattermost versions 11.7.x <= 11.7.2, 11.6.x <= 11.6.4, 10.11.x <= 10.11.19 fail to validate that an assigned incoming webhook user has access to the target team or channel, which allows a requester with webhook management permissions to create posts or direct messages attributed to another user via crafted incoming webhook configuration and payloads.. Mattermost Advisory ID: MMSA-2026-00683

Analysis

Technical impact

Mattermost versions 10.11.x up to 10.11.19, 11.6.x up to 11.6.4, and 11.7.x up to 11.7.2 improperly allow a configured incoming webhook to post or direct messages as an arbitrary user without checking that the webhook’s owner has access to the target team or channel. An attacker who has webhook‑management permissions can therefore craft webhook settings and payloads to impersonate other users. The weakness is an authorization flaw (CWE‑639).

Affected Systems

The vulnerability affects Mattermost installations running versions 10.11.0 through 10.11.19, 11.6.0 through 11.6.4, or 11.7.0 through 11.7.2. Upgrading to 10.11.20, 11.6.5, 11.7.3, or 11.8.0 or later removes the flaw.

Risk and Exploitability

The CVSS score of 4.9 classifies the issue as moderate severity. The EPSS score of < 1 % indicates a low probability of exploitation, and the vulnerability is not listed in CISA’s KEV catalog Exploitation requires the attacker to possess webhook‑management permissions within the Mattermost instance, after which they can construct a webhook configuration that masquerades messages under an arbitrary user’s identity.

Affected Products

Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).

Vendor Product Default status Versions

Mattermost

unaffected

Version	Status	Constraints
`11.7.0`	affected	≤ 11.7.2
`11.6.0`	affected	≤ 11.6.4
`10.11.0`	affected	≤ 10.11.19
`11.8.0`	unaffected	—
`11.7.3`	unaffected	—
`11.6.5`	unaffected	—
`10.11.20`	unaffected	—

Configuration 1 [-]

OR	cpe:2.3:a:mattermost:mattermost_server::::::::
	cpe:2.3:a:mattermost:mattermost_server::::::::
	cpe:2.3:a:mattermost:mattermost_server::::::::

No data.

Vendor Product Versions

Mattermost

Version	Status	Scheme	Platform
`[11.7.0,11.7.2]`	affected	semver	—
`[11.6.0,11.6.4]`	affected	semver	—
`[10.11.0,10.11.19]`	affected	semver	—
`11.8.0`	unaffected	semver	—
`11.7.3`	unaffected	semver	—
`11.6.5`	unaffected	semver	—
`10.11.20`	unaffected	semver	—

Remediation

Vendor Solution

Update Mattermost to versions 11.8.0, 11.7.3, 11.6.5, 10.11.20 or higher.

OpenCVE Recommended Actions

Apply the Mattermost update to versions 10.11.20, 11.6.5, 11.7.3, or 11.8.0 or later to eliminate the authorization bypass in incoming webhook handling.
Review all existing incoming webhook configurations to confirm that each webhook’s owner has legitimate access to the intended team or channel, and re‑configure or delete any that do not comply.
Restrict webhook‑management permissions to the smallest group of trusted roles and periodically audit these permissions to enforce least privilege for this sensitive capability.

Generated by OpenCVE AI on August 1, 2026 at 10:48 UTC.

Tracking

Advisories

No advisories available

Metrics

No CVSS v4.0

Attack Vector Network

Attack Complexity Low

Privileges Required High

Scope Unchanged

Confidentiality Impact None

Integrity Impact High

Availability Impact None

User Interaction None

No CVSS v3.0

No CVSS v2

This CVE is not in the KEV list.

Exploit prediction score: < 1% (0.361% probability within 30 days)

Exploitation none

Automatable no

Technical Impact partial

References

Link	Providers
https://mattermost.com/security-updates

History

Jul 13, 2026 3:30 PM Scoring metrics updated View changes

Type	Values Removed	Values Added
Metrics		ssvc `{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}`

Jul 13, 2026 9:45 AM First appearance in the feed. Affected vendors updated View changes

Type	Values Removed	Values Added
First Time appeared		Mattermost Mattermost mattermost
Vendors & Products		Mattermost Mattermost mattermost

Jul 13, 2026 8:45 AM Description updated. Title updated. Weaknesses updated. Added references. Scoring metrics updated View changes

Type	Values Removed	Values Added
Description		Mattermost versions 11.7.x <= 11.7.2, 11.6.x <= 11.6.4, 10.11.x <= 10.11.19 fail to validate that an assigned incoming webhook user has access to the target team or channel, which allows a requester with webhook management permissions to create posts or direct messages attributed to another user via crafted incoming webhook configuration and payloads.. Mattermost Advisory ID: MMSA-2026-00683
Title		Incoming webhook user attribution via unvalidated webhook owner
Weaknesses		CWE-639
References		https://mattermost.com/security-updates
Metrics		cvssV3_1 `{'score': 4.9, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:H/A:N'}`