Cyber Resilience

CVE-2026-9162

Mattermost Server 10.11.0 – 10.11.18

Published
22 June 2026
Modified
23 June 2026
Patch / advisory
View advisory
CVSS Score v3.1 4.3
Click a component to see what it means
Raw vectorCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
EPSS Score 0.0033 26th percentile
Risk Priority 36 floored blend · peak EPSS

Summary

CVE-2026-9162 is a medium-severity Insufficient Session Expiration (CWE-613) vulnerability in Mattermost Mattermost Server. Its CVSS base score is 4.3 (Medium).

Operationally, exploitation aligns with the MITRE ATT&CK technique Browser Session Hijacking (T1185); ranked at the 26th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.

The strongest mitigations our analysis identified map to AC-12 (Session Termination) — see the control section below for these in your framework.

OWASP Top 10 for Web (2025)

A07:2025 Authentication Failures

EU & UK References

Vulnerability Data

Mattermost versions 11.7.x <= 11.7.0, 11.6.x <= 11.6.2, 11.5.x <= 11.5.5, 10.11.x <= 10.11.17 fail to invalidate cached authentication state for active WebSocket connections during global session revocation, which allows a user with an existing WebSocket connection to remain authenticated…

more

and continue receiving real-time events until the cached session expires or the client reconnects.. Mattermost Advisory ID: MMSA-2026-00664

CWE(s)
CWE-613

Related Threats

MITRE ATT&CK Enterprise Techniques

T1185 Browser Session Hijacking Collection
Adversaries may take advantage of security vulnerabilities and inherent functionality in browser software to change content, modify user-behaviors, and intercept information as part of various browser session hijacking techniques.
attack.mitre.org →
T1550 Use Alternate Authentication Material Lateral Movement
Adversaries may use alternate authentication material, such as password hashes, Kerberos tickets, and application access tokens, in order to move laterally within an environment and bypass normal system access controls.
attack.mitre.org →
T1550.004 Web Session Cookie Lateral Movement
Adversaries can use stolen session cookies to authenticate to web applications and services.
attack.mitre.org →
T1563 Remote Service Session Hijacking Lateral Movement
Adversaries may take control of preexisting sessions with remote services to move laterally in an environment.
attack.mitre.org →
T1539 Steal Web Session Cookie Credential Access
An adversary may steal web application or service session cookies and use them to gain access to web applications or Internet services as an authenticated user without needing credentials.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2025-1412Same product: Mattermost Mattermost Server
CVE-2023-1421Same product: Mattermost Mattermost Server
CVE-2026-3495Same product: Mattermost Mattermost Server
CVE-2023-1776Same product: Mattermost Mattermost Server
CVE-2023-7113Same product: Mattermost Mattermost Server
CVE-2024-2445Same product: Mattermost Mattermost Server
CVE-2026-6339Same product: Mattermost Mattermost Server
CVE-2026-2457Same product: Mattermost Mattermost Server
CVE-2023-3581Same product: Mattermost Mattermost Server
CVE-2023-3591Same product: Mattermost Mattermost Server

Affected Assets

mattermost
mattermost server
10.11.0 — 10.11.18 · 11.5.0 — 11.5.6 · 11.6.0 — 11.6.3

Mitigating Controls

Mitigating Controls (NIST 800-53 r5) AI

AC-12 Session Termination good match

AC-12 directly requires automatic session termination after a defined period, structurally preventing reuse of expired session identifiers.

Mitigating Controls (NIST CSF 2.0) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.

PR.AA-01 mostly match
prevents

Credential lifecycle management directly includes enforcing session expiration to prevent reuse.

PR.AA-05 mostly match
prevents

Authorization policy enforcement and review covers terminating stale sessions to limit access scope.

PR.AA-03 partial match
prevents

Authentication mechanisms can incorporate session timeout checks but do not inherently address expiration policy.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

A.8.5 Secure authentication none match
none

Automatic termination of inactive sessions and limits on connection duration shrink the window during which a hijacked or unattended authenticated session can be exploited.

References