CVE-2025-1412 - How Mattermost’s User-to-Bot Session Failure Could Lead to Privilege Escalation

On June 2024, security researchers uncovered a serious vulnerability in Mattermost—a popular open-source messaging solution for workplaces and communities (official site). Tracked as CVE-2025-1412, the flaw affects certain versions and could allow attackers to keep improper session access—and even escalate privileges—after a user is converted from a regular account to a bot. In this post, we’ll break down what happened, how it works, and what it looks like in code, so you can understand why this bug matters and how to guard against it.

Mattermost 10.4.x (up to and including 10.4.1)

If you’re running these specific versions, your deployment is potentially at risk.

The Problem in Simple Terms

When a Mattermost admin _converts a user account to a bot_, all the old user’s login sessions should be invalidated. This would prevent any leftover "human" sessions from being used as a way to keep regular privileges, after the account "should" only be permitted bot activities.

Any previously active sessions (like those on a web browser or via an API token) stay alive.

- The former user, now technically a bot, can continue to act “as a full user” using those older sessions—even if the bot role has elevated privileges you never intended for a human!

How Does The Exploit Happen?

Let’s walk through a simplified attack scenario.

1. The Setup

Suppose Alice is a regular Mattermost user. An admin decides to convert Alice’s account into a _bot_ (for integrations or automation). Before the conversion, Alice’s browser and mobile app still have valid session cookies.

2. Conversion

The admin does the conversion through the UI or API—making Alice’s account a bot.

3. Sessions Stay Alive

Because of the bug, Alice’s previously existing sessions are NOT invalidated.

4. Alice Escalates

If the bot account assigned to Alice now has some elevated or unusual privileges (not all bots are created equal!), Alice can perform bot-level or even _user-level_ actions *from her active session*. She could access sensitive channels, send messages, or change configurations, all while technically being “just a bot.”

Intended behavior (pseudocode)

// When converting user to bot
func ConvertUserToBot(userID string) error {
    // ...conversion logic...
    InvalidateAllSessionsForUser(userID)
    return nil
}

Actual buggy behavior

// Conversion only changes user type, sessions left untouched
func ConvertUserToBot(userID string) error {
    // ...conversion logic...
    // MISSING: InvalidateAllSessionsForUser()
    return nil
}

Result:
The user’s old sessions (browser cookies, API tokens, etc.) continue to work. The system treats the session as “still logged in as old Alice,” even though the account is now a bot.

An admin (or attacker with some level of access) converts the user’s account to a bot.

3. Attacker uses their still-valid session to perform bot-level actions, or anything allowed by the bot’s permissions (including higher privileges if the bot is used for integrations).
4. No warning or logout occurs; session persists until forcibly logged out or expired by another means.

References

- Official Security Advisory (Mattermost)
- Mattermost Release Notes 9.11.x
- Mattermost Release Notes 10.4.x

If you’re running one of the affected versions

- Update Mattermost to the latest release in your branch, or preferably to the latest stable branch (9.11.7+, 10.4.2+, etc.).

Force logout all users after a user-to-bot conversion as an immediate workaround.

- Review all bots’ permission assignments. Ensure no regular user is inadvertently given bot roles with escalated privileges.

Best Practice:
Always ensure your login/session handling code invalidates all old sessions after a major account change (like user <-> bot conversions or role escalations).

Privilege escalation bugs like CVE-2025-1412 are especially dangerous in enterprise software

- Bot accounts often get more permissions by default (integration hooks, access to sensitive channels).
- An attacker can maintain unauthorized access, even after an admin “locks down” their normal account.

If your organization relies on Mattermost for internal discussions, leaks or privileged actions by an attacker could have real-world consequences.

Wrapping Up

CVE-2025-1412 shows how even well-known software can harbor hidden session management bugs. If you administer Mattermost, don’t overlook this flaw. Upgrade now, audit your bots, and always invalidate sessions on major account changes.

Stay safe. Update early. Monitor your logs for suspicious activity after any user-to-bot conversions.

If you found this breakdown helpful, follow Mattermost Security for more details and updates.

Timeline

Published on: 02/24/2025 08:15:09 UTC