CVE-2026-20796: Time-of-check time-of-use vulnerability in common teams API
Vulnerability summary
CVE-2026-20796 is a low (CVSS 3.1) vulnerability in mattermost. EPSS estimates a 0.22% chance of exploitation in the next 30 days, higher than 12.5% of scored vulnerabilities.
Not severe (CVSS 3.1, network access); no exploitation reported by the 5 checked sources
Source freshness unavailable
How is this decided?Advisory lineage
Upstream 0 · Downstream 2 · Related 2Timeline
- 13-02-2026PublishedVulnerability first disclosed.
- 13-02-2026Last modifiedVulnerability information updated.
Description
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 endpoint.. Mattermost Advisory ID: MMSA-2025-00549
CVSS metrics
3 scores · 3 sources · 1 version- OSV · GoEcosystem advisory · calculated3.1LowCVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:N
- NVDNIST3.1LowCVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:N
EPSS trend
Probability
0.22%
Chance of exploitation in the next 30 days
Percentile
13%
Versus all other CVEs
30-day change
Increase +0.01 pp
From 0.21% on 04-10-2026
Known exploited
Compare KEV catalogs
CISA KEVNot in the CISA KEV catalog.
ENISA CNWNot in the ENISA CNW catalog.
CIRCLNot in the CIRCL catalog.
Public exploits
0 foundNo public exploits indexed.
Weaknesses
CWE · root causeAffected systems
Known conditions: network-reachable, low-privilege account, no user interaction (CVSS vector). Other conditions: not stated in public data.
Mattermost2 products
- mattermost≥ 10.11.0, ≤ 10.11.9
- mattermost_server≥ 10.11.0, < 10.11.10
Github.com/mattermost1 product
- mattermost-server≥ 10.11.0, < 10.11.10 | ≥ 10.11.0+incompatible, < 10.11.10+incompatible
2 vendors · 3 products
