CVE-2026-6046
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedMattermost versions 11.6.x <= 11.6.1, 11.5.x <= 11.5.4, 10.11.x <= 10.11.15, 10.11.x <= 10.11.16 fail to validate that a username returned during bot registration belongs to a bot account, which allows an unprivileged attacker to intercept private messages sent by plugins via direct message channels by pre-registering a user account with a predictable plugin bot username.. Mattermost Advisory ID: MMSA-2026-00649
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceMattermost fails to validate that usernames submitted during bot registration belong to bot accounts. An unauthenticated attacker can pre-register a regular user account using a predictable plugin bot username, allowing them to intercept direct messages that plugins send through channels intended for those bot accounts.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data>= 10.11.0, < 10.11.17>= 11.5.0, < 11.5.5>= 11.6.0, < 11.6.2CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- High
- Privileges
- Low
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- None
- Availability
- None
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Identify installed Mattermost Server versionRun 'mattermost version' from the server CLI, or check the System Console under About > Mattermost Version, or inspect the /opt/mattermost/version fileAffected if The installed version falls within any of these ranges: 10.11.0 through 10.11.16, 11.5.0 through 11.5.4, or 11.6.0 through 11.6.1
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Verify user registration configurationNavigate to System Console > Authentication > Signup or check config.json for 'EnableSignUpWithEmail' and 'EnableOpenServer' settingsAffected if User self-registration is enabled (EnableSignUpWithEmail is true) and the server is open to unauthenticated signups (EnableOpenServer is true)
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Audit user accounts for plugin bot username patternsExport user list via System Console > Users > Export or use the CLI 'mattermost user list' and examine usernames for patterns matching known plugin bot naming conventions (typically prefixed with 'bot-', 'plugin-', or specific product names)Affected if Regular user accounts exist with usernames that match patterns typically used by system plugins (e.g., names that would be reserved for legitimate bot accounts)
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Review recent user account creation eventsCheck Mattermost logs in /var/log/mattermost/mattermost.log or System Console > Logs for new user creation events around the time of potential exploitation, or query the Users table for recently created accountsAffected if Multiple user accounts were created in short succession, or accounts were created with usernames matching known plugin bot identifiers
The environment is affected if the Mattermost Server version is within the affected ranges AND user self-registration is enabled, allowing unauthenticated attackers to register accounts with bot-like usernames.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
dbcve · scoped10.11.1711.5.511.6.2
Upgrade Mattermost to versions newer than 11.6.1, 11.5.4, and 10.11.15/16 per vendor advisory MMSA-2026-00649. If immediate patching is not feasible, audit existing user accounts for names matching known plugin bot patterns and monitor for unauthorized account creation.
Upgrade to Mattermost Server 10.11.17 (for 10.11.x line), 11.5.5 (for 11.5.x line), or 11.6.2 (for 11.6.x line)
- 1. Identify the current Mattermost Server version by checking the System Console > About page or running 'mmctl version'
- 2. For Mattermost 10.11.x versions: Upgrade to version 10.11.17 or later
- 3. For Mattermost 11.5.x versions: Upgrade to version 11.5.5 or later
- 4. For Mattermost 11.6.x versions: Upgrade to version 11.6.2 or later
- 5. After upgrade, verify the server is running the patched version in System Console > About
- 6. Test bot registration functionality to ensure proper validation is working
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation3.0 h
- Implementation6.0 h
- Testing3.0 h
- Review / QA2.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $3,984.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-6046 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-6046 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
- No spam, self-promotion, credentials, or personal data