Medium severity · published Oct 16, 2026
CVE-2026-19621
Mattermost leaks interactive-message integration secrets to non-admin users via post-deletion events and thread reads
6.5
CVSS
0.2%
EPSS
No
On KEV
Description
Mattermost versions 11.10.x <= 11.10.0, 11.7.x <= 11.7.9, 11.9.x <= 11.9.1, 11.8.x <= 11.8.5 fail to strip action integration secrets from post payloads before broadcasting post-deletion web socket events and returning thread API responses, which allows an authenticated channel member to obtain server-side webhook URLs and authentication context from interactive-message posts via the post_deleted websocket event or the threads REST API.. Mattermost Advisory ID: MMSA-2026-00766
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
Attack vector
Network
Complexity
Low
Privileges
Low
User interaction
None
Confidentiality
High
Integrity
None
Availability
None
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.2% · higher than 16% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
MA
Mattermost · Mattermost
11.10.0 through 11.10.0; 11.7.0 through 11.7.9; 11.9.0 through 11.9.1; 11.8.0 through 11.8.5 · source: vendor
MS
Mattermost Server · Mattermost
11.7.0 before 11.7.10; 11.8.0 before 11.8.6; 11.9.0 before 11.9.2; 11.10.0 · source: NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-19621
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-19621
mattermost.com
https://mattermost.com/security-updates
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