# CVE-2026-9708: Incoming webhook user attribution via unvalidated webhook owner

> CVE-2026-9708: Incoming webhook user attribution via unvalidated webhook owner. CVSS 4.9 (CVSS 3.1).

Canonical: https://rewindex.com/cve/CVE-2026-9708
Last updated: 2026-07-13T20:39:47Z

- Published: 2026-07-13 08:00 UTC · Updated: 2026-07-13 20:39 UTC · Assigner: Mattermost
- CVSS: 4.9 (CVSS 3.1) · Severity: Medium · Vector: CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:H/A:N
- EPSS: 0.36%, 30th percentile (scored 2026-10-25)
- CISA KEV: no
- CWE: CWE-639

## 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

## Affected vendors and products

- Mattermost: Mattermost

## Tracked companies

- [Mattermost](https://rewindex.com/company/mattermost.md)

## References

- [CVE record on cve.org](https://www.cve.org/CVERecord?id=CVE-2026-9708)
- [NVD entry](https://nvd.nist.gov/vuln/detail/CVE-2026-9708)
- [https://mattermost.com/security-updates](https://mattermost.com/security-updates)

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_Sources: CVE records from the CVE Program (cve.org). CVE® is a registered trademark of The MITRE Corporation. (https://www.cve.org/) This product uses data from the NVD API but is not endorsed or certified by the NVD. (https://nvd.nist.gov/) Known Exploited Vulnerabilities catalog from CISA. (https://www.cisa.gov/known-exploited-vulnerabilities-catalog) EPSS scores from FIRST (Exploit Prediction Scoring System). (https://www.first.org/epss/)_


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Canonical: https://rewindex.com/cve/CVE-2026-9708 · Markdown: https://rewindex.com/cve/CVE-2026-9708.md · JSON: https://rewindex.com/api/v1/cves/CVE-2026-9708 · Data licensed CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/) · Generated 2026-10-26T02:05:27.112Z