Cyber Resilience

CVE-2026-20796

Race Condition in Mattermost Server 10.11.0 – 10.11.10

Race Condition
Published
13 February 2026
Modified
23 February 2026
Patch / advisory
View advisory
CVSS Score v3.1 3.1
Click a component to see what it means
Raw vectorCVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:N
EPSS Score 0.0020 10th percentile
Risk Priority 15 floored blend · peak EPSS

Summary

CVE-2026-20796 is a low-severity Time-of-check Time-of-use (TOCTOU) Race Condition (CWE-367) vulnerability in Mattermost Mattermost Server. Its CVSS base score is 3.1 (Low).

Operationally, ranked at the 10th 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-3 (Access Enforcement) and AC-2 (Account Management) — see the control section below for these in your framework.

EU & UK References

Vulnerability Data

Mattermost versions 10.11.x <= 10.11.9 fail to properly validate channel membership at the time of data retrieval which allows a deactivated user to learn team names they should not have access to via a race condition in the /common_teams API…

more

endpoint.. Mattermost Advisory ID: MMSA-2025-00549

CWE(s)
CWE-367

Related Threats

MITRE ATT&CK Enterprise TechniquesAI

Insufficient information to map techniques.
Confidence: LOW · MITRE ATT&CK Enterprise v19.0

CVEs Like This One

CVE-2026-3590Same product: Mattermost Mattermost Server
CVE-2025-35965Same product: Mattermost Mattermost Server
CVE-2026-2325Same product: Mattermost Mattermost Server
CVE-2025-14822Same product: Mattermost Mattermost Server
CVE-2025-36530Same product: Mattermost Mattermost Server
CVE-2024-40884Same product: Mattermost Mattermost Server
CVE-2025-47871Same product: Mattermost Mattermost Server
CVE-2024-50052Same product: Mattermost Mattermost Server
CVE-2023-1777Same product: Mattermost Mattermost Server
CVE-2025-2571Same product: Mattermost Mattermost Server

Affected Assets

mattermost
mattermost server
10.11.0 — 10.11.10

Mitigating Controls

Control response

Prevent
Stop it (NIST 800-53)
  • AC-3 Access Enforcement
  • AC-2 Account Management
Detect
Catch it (NIST detect / respond)
  • SI-4 System Monitoring
Harden
Shrink the surface (DISA STIG)

—

Validate
Prove the fix (OWASP ASVS)
  • V15.4.2
  • V17.2.6

Mitigating Controls (NIST 800-53 r5) AI

AC-3 Access Enforcement good match
prevent

Directly enforces channel/team membership checks at every data retrieval point, eliminating the TOCTOU race that lets a deactivated user read unauthorized team names via /common_teams.

AC-2 Account Management partial match
prevent

Requires immediate disabling/revocation of all access rights for deactivated accounts so that even a transient race condition cannot return team data.

SI-4 System Monitoring partial match
detect

Monitors API calls for membership-validation anomalies or access attempts by deactivated identifiers, enabling detection of the race-condition exploitation.

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.PS-06 mostly match
prevents

Secure SDLC practices directly include coding standards and reviews that prevent TOCTOU race conditions.

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.8.17 Clock synchronization none match
none

Reliable, synchronized time across systems narrows the exploitable window in which a resource state can change between a security check and its use.

References