CVE-2026-27659

Mattermost CSRF in UpdateAccessControlPolicyActiveStatus: versions 11.2.x ≤ 11.2.2, 10.11.x ≤ 10.11.10, 11.4.x ≤ 11.4.0, 11.3.x ≤ 11.3.1 fail to validate CSRF tokens on /api/v4/access_control_policies/{policy_id}/activate, enabling an attacker to trick an admin into changing an access control pol...

CVE-2026-27659

Mattermost versions 11.2.x = 11.2.2, 10.11.x = 10.11.10, 11.4.x = 11.4.0, 11.3.x = 11.3.1 fail to properly validate CSRF tokens in the /api/v4/accesscontrolpolicies/policyid/activate endpoint, which allows an attacker to trick an admin into changing access control policy active status via a craft...

CVE-2026-27659 CSRF vulnerability in UpdateAccessControlPolicyActiveStatus endpoint

Mattermost versions 11.2.x = 11.2.2, 10.11.x = 10.11.10, 11.4.x = 11.4.0, 11.3.x = 11.3.1 fail to properly validate CSRF tokens in the /api/v4/accesscontrolpolicies/policyid/activate endpoint, which allows an attacker to trick an admin into changing access control policy active status via a craft...

CVE-2026-27659 CSRF vulnerability in UpdateAccessControlPolicyActiveStatus endpoint

Mattermost versions 11.2.x = 11.2.2, 10.11.x = 10.11.10, 11.4.x = 11.4.0, 11.3.x = 11.3.1 fail to properly validate CSRF tokens in the /api/v4/accesscontrolpolicies/policyid/activate endpoint, which allows an attacker to trick an admin into changing access control policy active status via a craft...

CVE-2026-27659 CSRF vulnerability in UpdateAccessControlPolicyActiveStatus endpoint

Mattermost versions 11.2.x = 11.2.2, 10.11.x = 10.11.10, 11.4.x = 11.4.0, 11.3.x = 11.3.1 fail to properly validate CSRF tokens in the /api/v4/accesscontrolpolicies/policyid/activate endpoint, which allows an attacker to trick an admin into changing access control policy active status via a craft...

CVE-2026-20719 DoS via URL Previews Rendering Malicious SVGs

Mattermost versions 11.4.x = 11.4.0, 11.3.x = 11.3.1, 11.2.x = 11.2.3, 10.11.x = 10.11.11 fail to prevent rendering of external SVGs on link embeds which allows unauthenticated users to crash the Mattermost webapp and desktop app via creating an issue or PR on GitHub.. Mattermost Advisory ID:...

CVE-2026-20719 DoS via URL Previews Rendering Malicious SVGs

Mattermost versions 11.4.x = 11.4.0, 11.3.x = 11.3.1, 11.2.x = 11.2.3, 10.11.x = 10.11.11 fail to prevent rendering of external SVGs on link embeds which allows unauthenticated users to crash the Mattermost webapp and desktop app via creating an issue or PR on GitHub.. Mattermost Advisory ID:...

CVE-2026-20719

CVE-2026-20719 affects Mattermost server/components that render external SVGs in link embeds across Mattermost 10.11.x–11.4.x (including 11.2.x, 11.3.x, 11.4.x). The root cause is failure to prevent rendering of external SVGs in embeds, enabling unauthenticated users to crash the web/desktop apps...

CVE-2026-20719 DoS via URL Previews Rendering Malicious SVGs

Mattermost versions 11.4.x = 11.4.0, 11.3.x = 11.3.1, 11.2.x = 11.2.3, 10.11.x = 10.11.11 fail to prevent rendering of external SVGs on link embeds which allows unauthenticated users to crash the Mattermost webapp and desktop app via creating an issue or PR on GitHub.. Mattermost Advisory ID:...

CVE-2026-27656 Account Takeover via Substring Matching in OpenID Connect Authentication

Mattermost versions 11.4.x = 11.4.0, 11.3.x = 11.3.1, 11.2.x = 11.2.3, 10.11.x = 10.11.11 fail to properly validate user identity in the OpenID IsSameUser comparison logic, which allows an attacker to take over arbitrary user accounts via an overly permissive substring matching flaw in the user...

CVE-2026-27656

Mattermost versions 11.4.x = 11.4.0, 11.3.x = 11.3.1, 11.2.x = 11.2.3, 10.11.x = 10.11.11 fail to properly validate user identity in the OpenID IsSameUser comparison logic, which allows an attacker to take over arbitrary user accounts via an overly permissive substring matching flaw in the user...

CVE-2026-27656

Mattermost contains a vulnerability (CVE-2026-27656) where versions 11.4.x <= 11.4.0, 11.3.x <= 11.3.1, 11.2.x <= 11.2.3, and 10.11.x

CVE-2026-27656 Account Takeover via Substring Matching in OpenID Connect Authentication

Mattermost versions 11.4.x = 11.4.0, 11.3.x = 11.3.1, 11.2.x = 11.2.3, 10.11.x = 10.11.11 fail to properly validate user identity in the OpenID IsSameUser comparison logic, which allows an attacker to take over arbitrary user accounts via an overly permissive substring matching flaw in the user...

CVE-2026-27656 Account Takeover via Substring Matching in OpenID Connect Authentication

Mattermost versions 11.4.x = 11.4.0, 11.3.x = 11.3.1, 11.2.x = 11.2.3, 10.11.x = 10.11.11 fail to properly validate user identity in the OpenID IsSameUser comparison logic, which allows an attacker to take over arbitrary user accounts via an overly permissive substring matching flaw in the user...

CVE-2026-26233 Denial of Service via HTTP/2 single packet attack on login endpoint

Mattermost versions 11.4.x = 11.4.0, 11.3.x = 11.3.1, 11.2.x = 11.2.3, 10.11.x = 10.11.11 fail to rate limit login requests which allows unauthenticated remote attackers to cause denial of service server crash and restart via HTTP/2 single packet attack with 100+ parallel login requests...

CVE-2026-26233 Denial of Service via HTTP/2 single packet attack on login endpoint

Mattermost versions 11.4.x = 11.4.0, 11.3.x = 11.3.1, 11.2.x = 11.2.3, 10.11.x = 10.11.11 fail to rate limit login requests which allows unauthenticated remote attackers to cause denial of service server crash and restart via HTTP/2 single packet attack with 100+ parallel login requests...

CVE-2026-26233

CVE-2026-26233 affects Mattermost releases 10.11.x to 11.4.x, where login requests are not rate-limited, enabling unauthenticated remote attackers to cause denial of service via an HTTP/2 single-packet attack with 100+ parallel login requests. No patch/version details are provided in the document...

Mattermost 安全漏洞

Mattermost is an open-source collaboration platform developed by the American company Mattermost. Vulnerabilities exist in versions of Mattermost 11.4.0 and earlier 11.4.x series, as well as versions prior to 11.3.1 11.3.x series, 11.2.3 and earlier 11.2.x series, and 10.11.11 and earlier 10.11.x...

PT-2026-27810

Name of the Vulnerable Software and Affected Versions Mattermost versions 11.4.0 and earlier Mattermost versions 11.3.1 and earlier Mattermost versions 11.2.3 and earlier Mattermost versions 10.11.11 and earlier Description The software does not properly prevent the rendering of external Scalable...

Mattermost 安全漏洞

Mattermost is an open-source collaboration platform developed by the American company Mattermost. Vulnerabilities exist in versions of Mattermost 11.4.0 and earlier 11.4.x series, as well as versions prior to 11.3.1 11.3.x series, 11.2.3 and earlier 11.2.x series, and 10.11.11 and earlier 10.11.x...