EUVD-2026-38247
GHSA-h998-hxxj-8q83
Severity by source
AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
Requires authenticated low-privileged session (PR:L); impact is confidentiality-only via continued event stream receipt; no integrity or availability consequence applies.
Primary rating from Vendor (Mattermost).
CVSS VectorVendor: Mattermost
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
Lifecycle Timeline
1DescriptionCVE.org
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 and continue receiving real-time events until the cached session expires or the client reconnects.. Mattermost Advisory ID: MMSA-2026-00664
AnalysisAI
WebSocket session persistence in Mattermost allows authenticated users whose sessions have been globally revoked to bypass that revocation and continue receiving real-time platform events. Affected across four actively maintained release branches (11.7.x, 11.6.x, 11.5.x, 10.11.x), the flaw directly undermines the effectiveness of administrative session revocation - a control relied upon in account-compromise response and offboarding workflows. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Exploitation requires a pre-existing, authenticated WebSocket connection to the Mattermost server that was established before the global session revocation event occurs. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The vendor-assigned CVSS score of 4.3 (Medium, vector AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N) accurately reflects the constrained impact: exploitation requires a pre-existing low-privileged authenticated session (PR:L), the scope is unchanged, and impact is limited to partial confidentiality with no integrity or availability consequence. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | A terminated employee or an attacker who has compromised a user account keeps their Mattermost desktop or browser client open and connected via WebSocket. An administrator triggers global session revocation as part of the incident response or offboarding process. … |
| Remediation | Upgrade to the patched Mattermost release for the applicable branch per vendor advisory MMSA-2026-00664, available at https://mattermost.com/security-updates. … Detailed patch versions, workarounds, and compensating controls in full report. |
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