# CVE-2026-19867: Uncapped mention keys in user notification properties allow CPU exhaustion during post processing

> CVE-2026-19867: Uncapped mention keys in user notification properties allow CPU exhaustion during post processing. CVSS 4.3 (CVSS 3.1).

Canonical: https://rewindex.com/cve/CVE-2026-19867
Last updated: 2026-10-16T19:23:18Z

- Published: 2026-10-16 07:00 UTC · Updated: 2026-10-16 19:23 UTC · Assigner: Mattermost
- CVSS: 4.3 (CVSS 3.1) · Severity: Medium · Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
- EPSS: 0.21%, 11th percentile (scored 2026-10-25)
- CISA KEV: no
- CWE: CWE-770

## Description

Mattermost versions 11.10.x \<= 11.10.0, 11.9.x \<= 11.9.1, 11.8.x \<= 11.8.5, 11.7.x \<= 11.7.10 fail to cap the number and size of mention keys stored in a user's notification properties, and to bound the quadratic multibyte-keyword matching performed for each post, which allows an authenticated user to degrade post-processing latency and consume excessive CPU on behalf of other members of any channel they share via storing an oversized notify\_props.mention\_keys list on their own profile.. Mattermost Advisory ID: MMSA-2026-00773

## 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-2026-19867)
- [NVD entry](https://nvd.nist.gov/vuln/detail/CVE-2026-19867)
- [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-2026-19867 · Markdown: https://rewindex.com/cve/CVE-2026-19867.md · JSON: https://rewindex.com/api/v1/cves/CVE-2026-19867 · Data licensed CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/) · Generated 2026-10-26T02:15:37.626Z