Mattermost Updates Fix Agents Plugin Replacement Flaw
Tech GuruQuick Answer
Mattermost CVE-2026-93851 affects maintained 11.7, 11.8, and 11.9 branches. Inventory servers and Agents plugin use, update to a listed fixed release, validate installed plugins and messaging, review administrator activity where warranted, and retain evidence.
Confirm Scope And Apply The Supported Remediation
What to do now: Inventory Mattermost servers, exact branch and build, Agents plugin installation and version, administrators, channel posting access, internet exposure, plugin inventory, owners, logs, and maintenance windows. Confirm an affected server branch and Agents plugin path; do not infer code execution from ordinary mentions, and do not assume an updated plugin alone fixes an affected server release. Upgrade to Mattermost 11.10.0, 11.9.2, 11.8.6, or 11.7.11 as appropriate, restrict plugin administration, and remove unauthorized plugin artifacts only after preserving evidence. Confirm the running release, enumerate installed plugin hashes and versions, test messaging, mentions, Agents functions and administration, review administrator and plugin events where warranted, and retain change evidence.
Last verified: 2026-10-29 UTC. Recheck the authoritative advisory and supported distribution channel before changing production.
Scope And Authority
| Product scope | Mattermost Server with the Agents plugin mention-reminder component |
|---|---|
| Advisory | Mattermost CVE-2026-93851 |
| CVE | CVE-2026-93851 |
| Authoritative release date | 2026-10-28 21:41:15.727 UTC |
| Authority revision date | 2026-10-28 21:41:15.727 UTC |
| Affected versions | Mattermost 11.9.0-11.9.1, 11.8.0-11.8.5, and 11.7.0-11.7.10. |
| Fixed version | Mattermost 11.10.0, 11.9.2, 11.8.6, or 11.7.11 |
| CVSS base score | 8.0 (CVSS v3.1) |
| CVSS severity | High |
| Exploitation status | Mattermost does not state that this vulnerability is being maliciously exploited.; no exploitation claim is inferred. |
What Changed
Mattermost fixed path traversal in the Agents plugin mention reminder that could make an administrator's browser replace an installed plugin, leading to server-side code execution.
What To Validate Now
- Inventory. Inventory Mattermost servers, exact branch and build, Agents plugin installation and version, administrators, channel posting access, internet exposure, plugin inventory, owners, logs, and maintenance windows.
- Establish applicability. Confirm an affected server branch and Agents plugin path; do not infer code execution from ordinary mentions, and do not assume an updated plugin alone fixes an affected server release.
- Remediate. Upgrade to Mattermost 11.10.0, 11.9.2, 11.8.6, or 11.7.11 as appropriate, restrict plugin administration, and remove unauthorized plugin artifacts only after preserving evidence.
- Validate. Confirm the running release, enumerate installed plugin hashes and versions, test messaging, mentions, Agents functions and administration, review administrator and plugin events where warranted, and retain change evidence.
- Retain evidence. Preserve asset and owner identifiers, the applicability decision, before-and-after versions, change approval, installation output, validation results, and any exception or rollback record.
Operational Cautions
Potential exploitation involves an administrator's browser and plugin replacement. Preserve server, audit and plugin evidence before remediation when unexpected plugin changes or crafted posts are found.
Evidence To Retain
- Exact product, release stream, package or application version, enabled feature, environment, and accountable owner.
- UTC timestamps, authority revision, approved change record, installer or package-manager output, and resulting version.
- Relevant logs and monitoring evidence, test results, exceptions, compensating controls, and rollback decisions.
Related TechGeeks Resources
Authoritative References
Correction policy: If the authority changes affected versions, fixed versions, severity, exploitation information, mitigations, or required action, TechGeeks will update this notice and its verification date.
