🛡️ CVE-2026-3495 — mattermost-server

How this vulnerability can be exploited

This issue can be reached over the network, attack complexity is low, an attacker needs administrative privileges on the target. No user interaction is required. The scope is unchanged, so the impact stays within the vulnerable component. Rated impact: confidentiality low, integrity low, availability none.

CVSS metrics in full

The score comes from this vector: CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:L/I:L/A:N

• Attack vector: Network — reachable from anywhere that can route to the service.
• Attack complexity: Low — the attack works reliably, with no preparation.
• Privileges required: High — administrative rights are needed first.
• User interaction: None — nobody has to be tricked into anything.
• Scope: Unchanged — the damage stays inside the vulnerable component.
• Confidentiality impact: Low — limited, and the attacker does not choose what is affected.
• Integrity impact: Low — limited, and the attacker does not choose what is affected.
• Availability impact: None.

Weakness class

CVE-2026-3495 is classified as CWE-79: Cross-site Scripting (XSS). User-supplied data is written into a page without escaping, so attacker script runs in the browser of anyone who views it.

Affected software

CVE-2026-3495 is recorded against 5 packages.

• github.com/mattermost/mattermost-server
• github.com/mattermost/mattermost-server/v5
• github.com/mattermost/mattermost-server/v6
• github.com/mattermost/mattermost/server/v8
• mattermost-server (from 11.5.0 up to 11.5.2)

Timeline and source

Published on 18 May 2026 and last revised on 25 June 2026. No public exploit is currently recorded for this entry. Record sourced from NVD.

References

nvd.nist.gov (Advisory)
github.com (Web)
github.com (Package)
mattermost.com (Web)

Other advisories for this package

github.com/mattermost/mattermost-server has other advisories on record. If you are patching this one, these are worth checking on the same host:

• CVE-2026-3473 (8.0 High, published 7 Jul 2026)
• CVE-2026-4646 (published 7 Jul 2026)
• CVE-2026-5755 (published 7 Jul 2026)
• CVE-2026-28735 (published 7 Jul 2026)
• CVE-2026-4635 (published 7 Jul 2026)
• CVE-2026-5308 (8.0 High, published 7 Jul 2026)
• CVE-2026-28759 (published 25 Jun 2026)
• CVE-2026-6347 (8.0 High, published 25 Jun 2026)

Same weakness in other software

These advisories are the same class of weakness (CWE-79: Cross-site Scripting (XSS)) in other software:

• CVE-2011-4924 (published 9 Jul 2026)
• CVE-2017-1000482 (published 9 Jul 2026)
• CVE-2017-20182 (published 7 Jul 2026)
• CVE-2021-3988 (published 7 Jul 2026)
• CVE-2014-0157 (published 6 Jul 2026)
• CVE-2017-1000426 (published 6 Jul 2026)
• CVE-2018-25045 (published 6 Jul 2026)
• CVE-2013-2209 (published 6 Jul 2026)

Details

Affected Packages

References