CVE-2026-8821

Mattermost versions 11.9.0, 11.8.4, 11.7.7, and 10.11.22 (and below within their respective branches) contain a permission bypass in the Playbooks feature. During playbook run creation, the system fails to validate the channel member-management permission, allowing an authenticated channel member...

CVE-2026-8821 Playbooks run owner channel membership permission bypass

Mattermost versions 11.9.x = 11.9.0, 11.8.x = 11.8.4, 11.7.x = 11.7.7, 10.11.x = 10.11.22 fail to validate channel member-management permission during playbook run creation, allowing an authenticated channel member to add an arbitrary user to a restricted channel via the run owner field...

CVE-2026-5132

Mattermost versions 11.9.x ≤ 11.9.0, 11.8.x ≤ 11.8.4, 11.7.x ≤ 11.7.7, and 10.11.x ≤ 10.11.22 fail to limit the size of unpacked SDP messages compressed with zlib in Calls WebSocket messages. An authenticated attacker (low privileges) can send many SDP messages that decompress to a large size, ca...

CVE-2026-5132 Unbounded zlib decompression in Calls SDP WebSocket messages

Mattermost versions 11.9.x = 11.9.0, 11.8.x = 11.8.4, 11.7.x = 11.7.7, 10.11.x = 10.11.22 fail to limit size of unpacked SDP messages compressed with zlib, which allows attacker to deny service or crash server via sending many SDP messages that unpack to large size.. Mattermost Advisory ID:...

EUVD-2026-77370

Mattermost versions 11.9.x = 11.9.0, 11.8.x = 11.8.4, 11.7.x = 11.7.7, 10.11.x = 10.11.22 fail to limit size of unpacked SDP messages compressed with zlib, which allows attacker to deny service or crash server via sending many SDP messages that unpack to large size.. Mattermost Advisory ID:...

CVE-2026-15814 Uploading a crafted image causes excessive memory allocation in the Mattermost Server

Mattermost versions 11.9.x = 11.9.0, 11.8.x = 11.8.4, 11.7.x = 11.7.7, 10.11.x = 10.11.22 fail to limit the amount of memory allocated when decoding uploaded image files which allows an authenticated user to cause excessive server memory consumption and potential denial of service via uploading a...

EUVD-2026-77369

Mattermost versions 11.9.x = 11.9.0, 11.8.x = 11.8.4, 11.7.x = 11.7.7, 10.11.x = 10.11.22 fail to limit the amount of memory allocated when decoding uploaded image files which allows an authenticated user to cause excessive server memory consumption and potential denial of service via uploading a...

CVE-2026-15814

Mattermost Server versions 11.9.x ≤ 11.9.0, 11.8.x ≤ 11.8.4, 11.7.x ≤ 11.7.7, and 10.11.x ≤ 10.11.22 fail to limit the amount of memory allocated when decoding uploaded image files. An authenticated user can cause excessive server memory consumption and potential denial of service by uploading a ...

CVE-2026-10542 Playbooks channel action update validation issue

Mattermost versions 11.9.x = 11.9.0, 11.8.x = 11.8.4, 11.7.x = 11.7.7, 10.11.x = 10.11.22 fail to validate channel action ownership which allows channel managers to update actions in other channels via the channel action update endpoint.. Mattermost Advisory ID: MMSA-2026-00692...

EUVD-2026-77366

Mattermost versions 11.9.x = 11.9.0, 11.8.x = 11.8.4, 11.7.x = 11.7.7, 10.11.x = 10.11.22 fail to validate channel action ownership which allows channel managers to update actions in other channels via the channel action update endpoint.. Mattermost Advisory ID: MMSA-2026-00692...

CVE-2026-10542

Mattermost versions 11.9.x ≤ 11.9.0, 11.8.x ≤ 11.8.4, 11.7.x ≤ 11.7.7, and 10.11.x ≤ 10.11.22 contain a validation flaw in the Playbooks channel action update endpoint . The failure to validate channel action ownership allows a channel manager to update actions belonging to other channels, leadin...

EUVD-2026-77364

Mattermost versions 11.9.x = 11.9.0, 11.8.x = 11.8.4, 11.7.x = 11.7.7, 10.11.x = 10.11.22 fail to enforce the board-creation permission which allows an unauthorized authenticated user to create boards via the board duplicate, boards-and-blocks, and archive-import endpoints.. Mattermost Advisory I...

CVE-2026-14344

Mattermost Boards endpoints in versions 11.9.x ≤ 11.9.0, 11.8.x ≤ 11.8.4, 11.7.x ≤ 11.7.7, and 10.11.x ≤ 10.11.22 fail to enforce the board-creation permission. An authenticated user without proper authorization can create boards via the board duplicate , boards-and-blocks , and archive-import en...

CVE-2026-12882

Mattermost is affected by a denial of service vulnerability in its Markdown autolink parsing (CVE-2026-12882, MMSA-2026-00703). The parser fails to handle autolinks with unmatched trailing closing parentheses in linear time, allowing an authenticated user with post-creation permission to trigger ...

CVE-2026-12882 Mattermost Markdown autolink parsing denial of service

Mattermost versions 11.9.x = 11.9.0, 11.8.x = 11.8.4, 11.7.x = 11.7.7, 10.11.x = 10.11.22 fail to parse Markdown autolinks with unmatched trailing closing parentheses in linear time, which allows an authenticated user with permission to create posts to cause excessive server CPU consumption and...

EUVD-2026-77363

Mattermost versions 11.9.x = 11.9.0, 11.8.x = 11.8.4, 11.7.x = 11.7.7, 10.11.x = 10.11.22 fail to parse Markdown autolinks with unmatched trailing closing parentheses in linear time, which allows an authenticated user with permission to create posts to cause excessive server CPU consumption and...

EUVD-2026-77361

Mattermost versions 11.9.x = 11.9.0, 11.8.x = 11.8.4, 11.7.x = 11.7.7, 10.11.x = 10.11.22 fail to properly enforce the limit of concurrent files being processed and handled failed files, which allows a user with permission to upload files to spawn more goroutines than intended and block the...

CVE-2026-11993

Mattermost versions 11.9.x ≤ 11.9.0 , 11.8.x ≤ 11.8.4 , 11.7.x ≤ 11.7.7 , and 10.11.x ≤ 10.11.22 are affected by a resource-exhaustion flaw in the file content indexing subsystem. The root cause is a failure to properly enforce the limit of concurrent files being processed and to handle failed fi...

CVE-2026-11993 Fix authenticated members disabling file content indexing server-wide via extraction pool exhaustion

Mattermost versions 11.9.x = 11.9.0, 11.8.x = 11.8.4, 11.7.x = 11.7.7, 10.11.x = 10.11.22 fail to properly enforce the limit of concurrent files being processed and handled failed files, which allows a user with permission to upload files to spawn more goroutines than intended and block the...

CVE-2026-14259

CVE-2026-14259 affects Mattermost versions 11.9.x ≤ 11.9.0, 11.8.x ≤ 11.8.4, 11.7.x ≤ 11.7.7, and 10.11.x ≤ 10.11.22. The board archive import feature fails to enforce team board creation permissions, allowing an authenticated non-guest team member to create Open or Private boards despite adminis...