CVE-2026-10106
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 11.7.x <= 11.7.2, 11.6.x <= 11.6.4, 10.11.x <= 10.11.19 fail to verify that the channel referenced in an action cookie matches the channel of the target post, which allows an authenticated user without access to a private channel to trigger interactive post actions on posts in that channel via a cookie obtained from any accessible channel.. Mattermost Advisory ID: MMSA-2026-00690
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 verify that the channel referenced in an action cookie matches the channel of the target post. This allows authenticated users to obtain an action cookie from an accessible channel and use it to trigger interactive post actions (reactions, replies, custom actions) on posts in private channels where they lack membership.
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, < 10.11.20>= 11.6.0, < 11.6.5>= 11.7.0, < 11.7.3CVSS 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
- Low
- Privileges
- Low
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- High
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/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.
-
Identify installed Mattermost Server versionRun 'mattermost version' from the server CLI, or check the /about endpoint in the system console, or inspect the version line in the mattermost config file under 'ServiceSettings'Affected if Version is 10.11.x before 10.11.20, 11.6.x before 11.6.5, or 11.7.x before 11.7.3
-
Verify interactive post actions feature is activeConfirm that reactions, post replies, or custom integrations using interactive messages are enabled in the system console under 'Site Configuration' > 'Posts' or via config.json 'ServiceSettings.EnablePostUsernameOverride' and related settingsAffected if Interactive post actions (reactions, replies, custom actions) are enabled and in use on the server
-
Check for private channels with cross-user accessIdentify private channels that contain some users but not all authenticated users; use SQL query on the database: SELECT COUNT(*) FROM Channels WHERE Type='P' AND (SELECT COUNT(*) FROM ChannelMembers WHERE ChannelId=Channels.Id) > 0Affected if Private channels exist where non-member authenticated users could potentially obtain action cookies from other accessible channels
-
Verify action cookie handling lacks channel validationExamine server logs for interactive post action requests where the channel_id in the action cookie differs from the channel_id of the target post; search logs for POST requests to /api/v4/posts/{post_id}/actions with unusual channel contextAffected if Action cookies from one channel are being successfully used to trigger actions on posts in private channels where the user is not a member
You are affected if your Mattermost Server version falls within 10.11.0-10.11.19, 11.6.0-11.6.4, or 11.7.0-11.7.2 AND interactive post actions are enabled AND private channels exist alongside accessible channels from which users can obtain action cookies.
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 · scoped10.11.2011.6.511.7.3
Upgrade to Mattermost versions 11.7.3, 11.6.5, or 10.11.20 or later to receive the patch. If patching is delayed, monitor for suspicious interactive post actions from users not members of the target channel.
Mattermost Server 10.11.20, 11.6.5, or 11.7.3 (depending on your major version branch)
- 1. Identify the currently installed Mattermost Server version using the system console or mmctl command
- 2. For Mattermost Server 10.11.x (10.11.0 - 10.11.19), upgrade to version 10.11.20 or later
- 3. For Mattermost Server 11.6.x (11.6.0 - 11.6.4), upgrade to version 11.6.5 or later
- 4. For Mattermost Server 11.7.x (11.7.0 - 11.7.2), upgrade to version 11.7.3 or later
- 5. Follow the standard Mattermost upgrade procedure: create a backup, stop the server, install the new version, restart the server, and verify functionality
- 6. After upgrade, verify that users cannot trigger interactive post actions on posts in private channels they do not have access to
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation2.0 h
- Implementation4.0 h
- Testing4.0 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 $3,328.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-10106 — 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-2026-10106 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
Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.
A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.
- 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