CVE-2026-4273 Insufficient token rotation validation in remote cluster invite confirmation
An authenticated attacker can bypass token rotation in remote cluster invites by reusing the original token, compromising the integrity of the invitation process.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-4273?
CVE-2026-4273 is a low-severity vulnerability in Mattermost Mattermost Server, published on 18 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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
Weakness: CWE-863
Which versions are affected by CVE-2026-4273?
12 open source packages ship an affected version, including github.com/mattermost/mattermost/server/v8, github.com/mattermost/mattermost-server and github.com/mattermost/mattermost-server/v5. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
github.com/mattermost/mattermost/server/v8 Go | All versions | 8.0.0-20260313190740-742e0be95074 |
github.com/mattermost/mattermost/server/v8 Go | All versions | 8.0.0-20260313190740-742e0be95074 |
github.com/mattermost/mattermost/server/v8 Go | All versions | 8.0.0-20260313190740-742e0be95074 |
github.com/mattermost/mattermost/server/v8 Go | From 10.11.0 | 10.11.14 |
github.com/mattermost/mattermost/server/v8 Go | From 10.11.0 | 10.11.14 |
github.com/mattermost/mattermost/server/v8 Go | From 11.5.0 | 11.5.2 |
6 more packages
github.com/mattermost/mattermost/server/v8 Go | From 11.5.0 | 11.5.2 |
github.com/mattermost/mattermost-server Go | All versions | 5.3.2-0.20260313190740-742e0be95074 |
github.com/mattermost/mattermost-server Go | All versions | 5.3.2-0.20260313190740-742e0be95074 |
github.com/mattermost/mattermost-server Go | From 10.11.0+incompatible | 10.11.14+incompatible, 11.5.2+incompatible |
github.com/mattermost/mattermost-server/v5 Go | All versions | None |
github.com/mattermost/mattermost-server/v6 Go | All versions | None |
Products include Mattermost Mattermost Server.
How do I fix CVE-2026-4273?
Upgrade github.com/mattermost/mattermost/server/v8 to a fixed version for your release line: 8.0.0-20260313190740-742e0be95074, 10.11.14 or 11.5.2.
Is CVE-2026-4273 being exploited?
There is no known exploitation of CVE-2026-4273 in the wild and no public exploit code.
Other vulnerabilities in Mattermost Mattermost Server
- CVE-2025-12419 Account takeover on OAuth/OpenID-enabled servers
- CVE-2025-12421 Account Takeover via Code Exchange Endpoint
- CVE-2025-4981 Path Traversal Leading to RCE by Any Authenticated Mattermost User
- CVE-2025-20051 Arbitrary file read via block duplication in Mattermost Boards
- CVE-2025-25279 Arbitrary file read in Mattermost Boards via import & export board archive
Sources
Also known as GHSA-hqpj-f3jh-29vx, GO-2026-5432.