CVE-2026-2455
March 16, 2026
Mattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 fail to canonicalize IPv4-mapped IPv6 addresses before reserved IP validation which allows an attacker to perform SSRF attacks against internal services via IPv4-mapped IPv6 literals (e.g., [::ffff:127.0.0.1]).. Mattermost Advisory ID: MMSA-2026-00585
Affected Packages
github.com/mattermost/mattermost-server (GO):
Affected version(s) >=v10.11.0-rc1 <v10.11.11Fix Suggestion:
Update to version v10.11.11github.com/mattermost/mattermost-server (GO):
Affected version(s) >=v11.2.0-rc1 <v11.2.3Fix Suggestion:
Update to version v11.2.3github.com/mattermost/mattermost/server/v8 (GO):
Affected version(s) >=v8.0.0-20230429093631-aac4f2337933 <v8.0.0-20260129133647-5d787969c2d5Fix Suggestion:
Update to version v8.0.0-20260129133647-5d787969c2d5github.com/mattermost/mattermost-server (GO):
Affected version(s) >=v11.3.0-rc1 <v11.3.1Fix Suggestion:
Update to version v11.3.1github.com/mattermost/mattermost (GO):
Affected version(s) =v11.3.0 <v11.3.1Fix Suggestion:
Update to version v11.3.1github.com/mattermost/mattermost (GO):
Affected version(s) >=v11.2.0 <v11.2.3Fix Suggestion:
Update to version v11.2.3github.com/mattermost/mattermost (GO):
Affected version(s) >=v10.11.0 <v10.11.11Fix Suggestion:
Update to version v10.11.11Related Resources (5)
Do you need more information?
Contact UsCVSS v4
Base Score:
5.3
Attack Vector
NETWORK
Attack Complexity
LOW
Attack Requirements
NONE
Privileges Required
LOW
User Interaction
NONE
Vulnerable System Confidentiality
LOW
Vulnerable System Integrity
NONE
Vulnerable System Availability
NONE
Subsequent System Confidentiality
NONE
Subsequent System Integrity
NONE
Subsequent System Availability
NONE
CVSS v3
Base Score:
4.3
Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
LOW
User Interaction
NONE
Scope
UNCHANGED
Confidentiality
LOW
Integrity
NONE
Availability
NONE
Weakness Type (CWE)
Server-Side Request Forgery (SSRF)
EPSS
Base Score:
0.03
