Medium severity · published Jun 12, 2026
CVE-2026-6046
Plugin bot username conflict allows user account to be used as bot identity in Mattermost Server
5.3
CVSS
0.2%
EPSS
No
On KEV
Description
Mattermost versions 11.6.x <= 11.6.1, 11.5.x <= 11.5.4, 10.11.x <= 10.11.15, 10.11.x <= 10.11.16 fail to validate that a username returned during bot registration belongs to a bot account, which allows an unprivileged attacker to intercept private messages sent by plugins via direct message channels by pre-registering a user account with a predictable plugin bot username.. Mattermost Advisory ID: MMSA-2026-00649
CVSS vector
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N
Attack vector
Network
Complexity
High
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 9% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
MA
Mattermost · Mattermost
11.6.0 through 11.6.1; 11.5.0 through 11.5.4; 10.11.0 through 10.11.15; 10.11.0 through 10.11.16 · source: vendor
MS
Mattermost Server · Mattermost
10.11.0 before 10.11.17; 11.5.0 before 11.5.5; 11.6.0 before 11.6.2 · source: NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-6046
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-6046
Vendor Advisory
https://mattermost.com/security-updates
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