How severe is CVE-2026-8823?

CVE-2026-8823 has a CVSS 3.x base score of 3.8, rated low severity. It is exploitable over network with low attack complexity, requires high privileges and no user interaction. Impact on confidentiality is none, integrity low, and availability low.

Is CVE-2026-8823 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (14th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-8823?

CVE-2026-8823 affects Mattermost Mattermost Server. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-8823?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

Does CVE-2026-8823 have an EU (EUVD) identifier?

Yes. CVE-2026-8823 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-38276.

When was CVE-2026-8823 published?

CVE-2026-8823 was published on 2026-06-22 and last updated on 2026-06-26.

CVE-2026-8823

CVE-2026-8823 is a low-severity vulnerability in Mattermost Mattermost Server with a CVSS 3.x base score of 3.8. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-863.

Key facts

Severity: Low (CVSS 3.x base score 3.8)
EPSS exploit prediction: 0% (14th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-38276
Weakness: CWE-863
Affected product: Mattermost Mattermost Server
Published: 2026-06-22
Last modified: 2026-06-26

Description

Mattermost versions 11.7.x <= 11.7.0, 10.11.x <= 10.11.17 fail to validate bot targets when demoting users to guests which allows a lower-privileged administrator to degrade arbitrary bot accounts via the standard demote-user API.. Mattermost Advisory ID: MMSA-2026-00669

Frequently asked questions

What is CVE-2026-8823?: Mattermost versions 11.7.x <= 11.7.0, 10.11.x <= 10.11.17 fail to validate bot targets when demoting users to guests which allows a lower-privileged administrator to degrade arbitrary bot accounts via the standard demote-user API.. Mattermost Advisory ID: MMSA-2026-00669
How severe is CVE-2026-8823?: CVE-2026-8823 has a CVSS 3.x base score of 3.8, rated low severity. It is exploitable over network with low attack complexity, requires high privileges and no user interaction. Impact on confidentiality is none, integrity low, and availability low.
Is CVE-2026-8823 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (14th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-8823?: CVE-2026-8823 affects Mattermost Mattermost Server. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-8823?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2026-8823 have an EU (EUVD) identifier?: Yes. CVE-2026-8823 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-38276.
When was CVE-2026-8823 published?: CVE-2026-8823 was published on 2026-06-22 and last updated on 2026-06-26.

References

https://mattermost.com/security-updates

Affected products (1)

cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*

More vulnerabilities in Mattermost Mattermost Server

CVE-2025-12421 — Critical (CVSS 9.9): Mattermost versions 11.0.x <= 11.0.2, 10.12.x <= 10.12.1, 10.11.x <= 10.11.4, 10.5.x <= 10.5.12 fail to to verify that…
CVE-2025-12419 — Critical (CVSS 9.9): Mattermost versions 10.12.x <= 10.12.1, 10.11.x <= 10.11.4, 10.5.x <= 10.5.12, 11.0.x <= 11.0.3 fail to properly…
CVE-2025-4981 — Critical (CVSS 9.9): Mattermost versions 10.5.x <= 10.5.5, 9.11.x <= 9.11.15, 10.8.x <= 10.8.0, 10.7.x <= 10.7.2, 10.6.x <= 10.6.5 fail to…
CVE-2025-25279 — Critical (CVSS 9.9): Mattermost versions 10.4.x <= 10.4.1, 9.11.x <= 9.11.7, 10.3.x <= 10.3.2, 10.2.x <= 10.2.2 fail to properly validate…
CVE-2025-20051 — Critical (CVSS 9.9): Mattermost versions 10.4.x <= 10.4.1, 9.11.x <= 9.11.7, 10.3.x <= 10.3.2, 10.2.x <= 10.2.2 fail to properly validate…
CVE-2017-18920 — Critical (CVSS 9.8): An issue was discovered in Mattermost Server before 3.6.2. The WebSocket feature does not follow the Same Origin Policy.

All CVEs affecting Mattermost Mattermost Server →

Other CWE-863 (Incorrect Authorization) vulnerabilities

CVE-2026-48286 — Critical (CVSS 10.0): Adobe Campaign Classic (ACC) versions 7.4.3 build 9396 and earlier are affected by an Incorrect Authorization…
CVE-2026-48303 — Critical (CVSS 10.0): Adobe Campaign Classic (ACC) versions 7.4.3 build 9394 and earlier are affected by an Incorrect Authorization…
CVE-2026-44330 — Critical (CVSS 10.0): free5GC is an open-source implementation of the 5G core network. Prior to 4.2.2, free5GC's NEF mounts the…
CVE-2026-46595 — Critical (CVSS 10.0): Previously, CVE-2024-45337 fixed an authorization bypass for misused ssh server configurations; if any other type of…
CVE-2026-33105 — Critical (CVSS 10.0): Improper authorization in Microsoft Azure Kubernetes Service allows an unauthorized attacker to elevate privileges over…
CVE-2026-32213 — Critical (CVSS 10.0): Improper authorization in Azure AI Foundry allows an unauthorized attacker to elevate privileges over a network.

Browse all CWE-863 (Incorrect Authorization) vulnerabilities →