CVE-2026-20796

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{}

{"affected": [{"configurations": [{"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "[10.11.0,10.11.9]"}}, {"platform": null, "status": "unaffected", "versions": {"scheme": "semver", "value": "11.3.0"}}, {"platform": null, "status": "unaffected", "versions": {"scheme": "semver", "value": "10.11.10"}}], "product": "mattermost", "vendor": "mattermost"}], "analysis": {"en": {"generated_at": "2026-04-17T19:54:06.886570+00:00", "value": {"mitigation_remediation": ["Apply the vendor\u2011recommended patch by upgrading Mattermost to version 10.11.10 or higher, or to 11.3.0 or later.", "If immediate upgrading is not feasible, restrict the /common_teams API endpoint so that deactivated users cannot access it, for example by configuring access policies or using a firewall rule.", "Monitor system logs for repeated requests to /common_teams from deactivated accounts and investigate any anomalies."], "summary": {"action": "Patch", "impact": "Information disclosure through a race condition in the /common_teams API that allows a deactivated user to discover unauthorized team names."}, "threat_synthesis": {"affected_systems": "Sponsors: Mattermost, product: Mattermost server. Affected versions are 10.11.0 through 10.11.9 inclusive; the vendor recommends upgrading to 10.11.10 or higher, or to 11.3.0 or later.", "description_and_impact": "The vulnerability resides in Mattermost server versions 10.11.x from 10.11.0 to 10.11.9, where the /common_teams endpoint fails to validate channel membership at the time data is retrieved. A deactivated user can exploit a race condition to learn the names of teams they should not be able to see, resulting in unauthorized disclosure of sensitive team information. The weakness corresponds to CWE\u2011367 and carries a low CVSS score of 3.1.", "risk_and_exploitability": "The CVSS base score of 3.1 and an EPSS rate of less than 1% indicate a low likelihood of exploitation. The vulnerability is not listed in the CISA Known Exploited Vulnerabilities catalog. Exploitation would require an attacker to have a deactivated account that can still call the /common_teams API, then repeatedly invoke the endpoint during the presence of a race condition; based on the description, the attack vector is likely remote API usage by a compromised or malicious deactivated user."}}}}, "created": "2026-02-13T21:28:43.226353+00:00", "updated": "2026-04-17T20:00:09.020522+00:00", "vendors": ["mattermost", "mattermost$PRODUCT$mattermost"]}