Vulnerability · Published May 18, 2026 · Assigned by Mattermost
CVE-2026-3495Unescaped variables during error page composition
Low 3.8
In plain English
A low-severity cross-site scripting in Mattermost from Mattermost. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.1% (higher than 4% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13 fail to escape some variables that could contain malicious content during error page composition which allows an attacker with access to edit some site configuration to execute some malicious code via injecting some JS as part of those values.. Mattermost Advisory ID: MMSA-2026-00622
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Go | github.com/mattermost/mattermost-server | 10.11.14+incompatible, 11.5.2+incompatible | GO-2026-5484 |
| Go | github.com/mattermost/mattermost-server | 5.3.2-0.20260310115442-5a1ea95044dc | GHSA-jx93-pf6x-874r |
| Go | github.com/mattermost/mattermost-server/v5 | no fix listed | GO-2026-5484 |
| Go | github.com/mattermost/mattermost-server/v6 | no fix listed | GO-2026-5484 |
| Go | github.com/mattermost/mattermost/server/v8 | no fix listed | GO-2026-5484 |
| Go | github.com/mattermost/mattermost/server/v8 | 11.5.2 | GHSA-jx93-pf6x-874r |
| Go | github.com/mattermost/mattermost/server/v8 | 8.0.0-20260310115442-5a1ea95044d | GHSA-jx93-pf6x-874r |
| Go | github.com/mattermost/mattermost/server/v8 | 10.11.14 | GHSA-jx93-pf6x-874r |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| Mattermost | Mattermost | 11.5.0 – through 11.5.110.11.0 – through 10.11.13 |
Weakness: CWE-79 · Vector: CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:L/I:L/A:N
References
- MMSA-2026-00622 vendor-advisory