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 27 floored blend · peak EPSS

CVSS and EPSS are reproduced from their sources (NVD, FIRST EPSS). Risk Priority is our own derived reading, not an NVD score.

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, exploitation aligns with the MITRE ATT&CK technique Path Interception (T1034); 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-25 (Reference Monitor) and AC-3 (Access Enforcement) — 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 Techniques

T1034 Path Interception Persistence
**This technique has been deprecated.
attack.mitre.org →
T1548 Abuse Elevation Control Mechanism Privilege Escalation
Adversaries may circumvent mechanisms designed to control privilege elevation to gain higher-level permissions.
attack.mitre.org →
T1574 Hijack Execution Flow Stealth
Adversaries may execute their own malicious payloads by hijacking the way operating systems run programs.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2026-3590Same product: Mattermost Mattermost Server
CVE-2025-4981Same product: Mattermost Mattermost Server
CVE-2026-6689Same product: Mattermost Mattermost Server
CVE-2026-10085Same product: Mattermost Mattermost Server
CVE-2025-58073Same product: Mattermost Mattermost Server
CVE-2024-50052Same product: Mattermost Mattermost Server
CVE-2025-58075Same product: Mattermost Mattermost Server
CVE-2025-14350Same product: Mattermost Mattermost Server
CVE-2025-41443Same product: Mattermost Mattermost Server
CVE-2026-2463Same 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)

—

Detect
Catch it (NIST detect / respond)

—

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-25 Reference Monitor good match

A reference monitor that is always invoked and analyzable structurally eliminates the non-atomic check-then-use pattern underlying TOCTOU.

AC-3 Access Enforcement partial match

Access enforcement that performs an atomic check-and-use decision directly stops the window in which a TOCTOU race can be exploited.

SC-39 Process Isolation partial match

Process isolation limits the blast radius of a successful TOCTOU exploitation but does not remove the race itself.

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.

References