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Vulnerabilities associated with github.com/mattermost/mattermost-server.

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Showing 25 vulnerabilities on this page for github.com/mattermost/mattermost-server

Signals CISA KEV Ransomware Nuclei
VulnerabilityTitle and contextCVSSEPSSPoCsSignals

Server panic via outgoing webhook responses

Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to filter nil elements from outgoing webhook attachment payloads before processing, which allows an authenticated user to cause a denial of service (server process termination) via a crafted webhook callback response containing a null attachment entry.. Mattermost Advisory ID: MMSA-2026-00641

CWE-754May 25, 2026
CVSS6.5v3.1EPSS0.277%PoCs0SignalsSTIX

GitHub OAuth Scope Validation

Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to validate the OAuth token scope on the callback which allows an authenticated Mattermost user to gain access to private repositories via modifying the scope parameter in the GitHub authorization URL.. Mattermost Advisory ID: MMSA-2026-00628

CWE-863May 22, 2026
CVSS5.4v3.1EPSS0.138%PoCs0SignalsSTIX

Persistent notification timing attack causing server denial of service

Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to archive the channel before removing persistent notifications which allows authenticated user to crash the server via timing the creation of persistent notification message between the server deleting existing persistent notifications and archiving the channel.. Mattermost Advisory ID: MMSA-2026-00637

CWE-362May 22, 2026
CVSS6.5v3.1EPSS0.172%PoCs0SignalsSTIX

Improper file ownership validation in the Boards API allows unauthorised file access

Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to validate file ownership and access control, which allows an authenticated user to access and download files belonging to other users or teams via crafted Boards API requests using valid file IDs.. Mattermost Advisory ID: MMSA-2026-00620

CWE-639May 22, 2026
CVSS5.9v3.1EPSS0.149%PoCs0SignalsSTIX

Insufficient input validation in GitHub plugin API causes denial of service

Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to validate user-supplied input in API request handlers which allows an authenticated attacker to crash the plugin process via a crafted HTTP request to the PR details endpoint.. Mattermost Advisory ID: MMSA-2026-00638

CWE-1287May 22, 2026
CVSS4.3v3.1EPSS0.25%PoCs0SignalsSTIX

Sanitize team member data returned by API

Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to sanitize team member data when returned via API to users without elevated permissions which allows a user without permissions to get data about team members roles via invoking various team API endpoints.. Mattermost Advisory ID: MMSA-2026-00626

CWE-200May 22, 2026
CVSS4.3v3.1EPSS0.184%PoCs0SignalsSTIX

Unauthenticated WebSocket binary frame causes denial of service in Mattermost Server

Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to properly validate msgpack-encoded WebSocket frames before memory allocation which allows an unauthenticated remote attacker to crash the server process and cause a full service outage for all users via a crafted binary WebSocket message sent to the public WebSocket endpoint.. Mattermost Advisory ID: MMSA-2026-00647

CWE-789May 22, 2026
CVSS7.5v3.1EPSS0.34%PoCs0SignalsSTIX

Missing request body size limits on Zoom plugin HTTP endpoints

Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to enforce request body size limits on plugin HTTP endpoints which allows an attacker to cause a denial of service via crafted oversized HTTP requests.. Mattermost Advisory ID: MMSA-2026-00646

CWE-400May 22, 2026
CVSS4.9v3.1EPSS0.254%PoCs0SignalsSTIX

Denial of service via crafted TIFF file upload

Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.2, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to validate the TIFF IFD offset in the image header before allocating memory, which allows authenticated users with file upload or posting permissions to cause a denial of service (server OOM) via uploading a crafted TIFF file or posting a URL that serves one.. Mattermost Advisory ID: MMSA-2026-00648

CWE-400May 22, 2026
CVSS6.5v3.1EPSS0.245%PoCs0SignalsSTIX

Path traversal in integration action URL leading to arbitrary API execution via system admin’s auth token.

Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to check integration URL for path traversal which allows an malicious authenticated user to call an arbitrary API via system admin Mattermost auth token using via path traversal in integration action URL.. Mattermost Advisory ID: MMSA-2026-00640

CWE-22May 21, 2026
CVSS8.0v3.1EPSS0.327%PoCs0SignalsSTIX

SSRF via Host Header Spoofing in Custom Slash Commands

Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13 fail to validate the Host header when constructing response URLs for custom slash commands which allows an authenticated attacker to redirect slash command responses to an attacker-controlled server via a spoofed Host header.. Mattermost Advisory ID: MMSA-2026-00582

CWE-918May 18, 2026
CVSS3.5v3.1EPSS0.137%PoCs0SignalsSTIX

Prevent password disclosure and force reset during Slack import

Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13, 11.4.x <= 11.4.3 fail prevent disclosure of created user password which allows a malicious attacker to impersonate a user via the use of some of those passwords.. Mattermost Advisory ID: MMSA-2026-00614

CWE-522May 18, 2026
CVSS6.5v3.1EPSS0.231%PoCs0SignalsSTIX

Sensitive credentials exposed in plaintext in Mattermost support packets

Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13, 11.4.x <= 11.4.3 fail to sanitize sensitive configuration fields before including them in support packet generation, which allows a Mattermost System Admin or any party with access to a support packet to obtain sensitive credentials in plaintext via downloading a support packet from the System Console.. Mattermost Advisory ID: MMSA-2026-00607

CWE-200May 18, 2026
CVSS8.7v3.1EPSS0.301%PoCs0SignalsSTIX

Slash command trigger-word update allowed command hijacking

Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13, 11.4.x <= 11.4.3 Fail to enforce slash command trigger-word uniqueness during command updates which allows an authenticated team member with Manage Own Slash Commands permission to hijack and impersonate existing system or custom slash commands via editing their own slash command trigger to an already-registered trigger through the command update API. Mattermost Advisory ID: MMSA-2026-00597

CWE-863May 18, 2026
CVSS4.3v3.1EPSS0.152%PoCs0SignalsSTIX

Mattermost Calls plugin exposes TURN server credentials in plaintext in support packets

Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13, 11.4.x <= 11.4.3 fail to sanitize sensitive configuration fields in the Mattermost Calls plugin which allows an attacker with access to a support packet to obtain TURN server credentials via the plaintext values present in the exported plugin configuration.. Mattermost Advisory ID: MMSA-2026-00605

CWE-200May 18, 2026
CVSS7.6v3.1EPSS0.266%PoCs0SignalsSTIX

Missing authorization check in AI message rewrite endpoint allows access to private thread content

Mattermost versions 11.5.x <= 11.5.1 fail to verify channel membership when processing AI-assisted message rewrites which allows an authenticated attacker to read the content of threads in private channels and direct messages they do not have access to via a crafted request to the post rewrite endpoint.. Mattermost Advisory ID: MMSA-2026-00645

CWE-862May 18, 2026
CVSS6.5v3.1EPSS0.205%PoCs0SignalsSTIX

Missing request origin validation on burn-on-read reveal endpoint

Mattermost versions 11.5.x <= 11.5.1, 11.4.x <= 11.4.3 fail to validate the X-Requested-With header on the burn-on-read reveal endpoint which allows an authenticated channel member to force the reveal of a burn-on-read message without recipient consent via a crafted Markdown image tag.. Mattermost Advisory ID: MMSA-2026-00636

CWE-346May 18, 2026
CVSS4.3v3.1EPSS0.113%PoCs0SignalsSTIX

Memory Exhaustion via Malicious 7zip File Upload

Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13, 11.4.x <= 11.4.3 fail to validate 7zip archive structure before processing which allows an authenticated attacker to cause server memory exhaustion and denial of service via uploading a specially crafted 7zip file with excessive folder declarations.. Mattermost Advisory ID: MMSA-2026-00573

CWE-789May 18, 2026
CVSS4.3v3.1EPSS0.24%PoCs0SignalsSTIX

Unescaped variables during error page composition

Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13 fail to escape some variables that could contain malicious content during error page composition which allows an attacker with access to edit some site configuration to execute some malicious code via injecting some JS as part of those values.. Mattermost Advisory ID: MMSA-2026-00622

CWE-79May 18, 2026
CVSS3.8v3.1EPSS0.143%PoCs0SignalsSTIX

Insufficient token rotation validation in remote cluster invite confirmation

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

CWE-863May 18, 2026
CVSS3.7v3.1EPSS0.142%PoCs0SignalsSTIX

Mattermost fails to enforce create_post permission when editing posts

Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13, 11.4.x <= 11.4.3 fail to check the create_post channel permission during post edit operations which allows an authenticated attacker with revoked posting privileges to modify their existing posts via direct API requests to the post update and patch endpoints.. Mattermost Advisory ID: MMSA-2026-00627

CWE-862May 18, 2026
CVSS4.3v3.1EPSS0.152%PoCs0SignalsSTIX

Improper Input Validation in MS Teams Meetings API Handler

Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13, 11.4.x <= 11.4.3 fail to limit the size of the request body on the start meeting API endpoint, which allows an authenticated attacker to cause resource exhaustion or denial of service via a crafted oversized HTTP POST request to {{/api/v1/meetings}}.. Mattermost Advisory ID: MMSA-2026-00608

CWE-770May 18, 2026
CVSS4.3v3.1EPSS0.24%PoCs0SignalsSTIX

Insufficient authorization in shared channel membership sync allows remote cluster to remove users from arbitrary channels

Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13, 11.4.x <= 11.4.3 fail to validate that a remote cluster has access to a channel before processing membership removal requests during shared channel membership sync, which allows a malicious remote cluster to remove any user from any channel, including private channels, via crafted membership sync messages targeting channels the remote cluster is not authorized to access. Mattermost Advisory ID: MMSA-2026-00576

CWE-863May 18, 2026
CVSS4.3v3.1EPSS0.152%PoCs0SignalsSTIX

OAuth authorization code client binding not enforced during token redemption in Mattermost

Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13 fail to enforce client identity binding during the OAuth authorization code redemption flow which allows an authenticated OAuth client to redeem authorization codes issued to a different client via a crafted token exchange request.. Mattermost Advisory ID: MMSA-2026-00570

CWE-305May 18, 2026
CVSS3.1v3.1EPSS0.118%PoCs0SignalsSTIX

post edit time limit is not enforced on some post update operations

Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13 fail to enforce the PostEditTimeLimit on non-message post fields which allows an authenticated user to modify post file attachments, props, and pin status after the edit window has expired via the post patch and update API endpoints.. Mattermost Advisory ID: MMSA-2026-00631

CWE-672May 15, 2026
CVSS3.1v3.1EPSS0.165%PoCs0SignalsSTIX