Mattermost has session spoofing due to lack of single-use consumption of guest magic link tokens enforcement

CVE-2026-3590 → View on GitHub ↗ View on CVE.org ↗ View on NVD ↗

Description

Mattermost versions 10.11.x <= 10.11.12, 11.5.x <= 11.5.0, 11.4.x <= 11.4.2, 11.3.x <= 11.3.2 fail to enforce atomic single-use consumption of guest magic link tokens, which allows an attacker with access to a valid magic link to establish multiple independent authenticated sessions via concurrent requests. Mattermost Advisory ID: MMSA-2026-00624.

Basic information

Type
reviewed
Severity
medium
Advisory on GitHub
Open advisory ↗
Repository advisory
—
Source code
Browse source ↗
Published (advisory)
2026-04-17 15:31:17 UTC
Updated
2026-04-28 22:57:44 UTC
GitHub reviewed
2026-04-28 22:57:43 UTC
NVD published
2026-04-15

EPSS Score

Score Percentile
0.03% 10.21%

CVSS Scores

Base score Version Severity Vector
6.5 3.1 —
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:L)
Some sensitive info could get out, but not a total data dump.
Integrity (I:L)
Attackers could change some data, but it’s limited—not everything goes.
Availability (A:N)
Service keeps running; no real outage angle.

Identifiers

Type Value
GHSA GHSA-mh4x-rmrx-3hp4 ↗
CVE CVE-2026-3590 ↗

CWEs

CWE id Name
CWE-367 Time-of-check Time-of-use (TOCTOU) Race Condition

Affected packages (5)

Vulnerable version ranges and first patched releases as published by GitHub.

Ecosystem Package Vulnerable range First patched Vulnerable functions
go github.com/mattermost/mattermost/server/v8 >= 8.0.0-20250721062209-4952acea88ce, < 8.0.0-20250723052842-4cb8d8940332 8.0.0-20250723052842-4cb8d8940332 —
go github.com/mattermost/mattermost-server >= 10.11.0-rc1, < 10.11.13 10.11.13 —
go github.com/mattermost/mattermost-server = 11.5.0-rc1 11.5.0 —
go github.com/mattermost/mattermost-server >= 11.4.0-rc1, < 11.4.3 11.4.3 —
go github.com/mattermost/mattermost-server >= 11.3.0-rc1, < 11.3.3 11.3.3 —

References

cvelogic Threat Intelligence