CVE-2026-2455
Received Received - Intake
SSRF Vulnerability in Mattermost via IPv4-Mapped IPv6 Address Handling

Publication date: 2026-03-16

Last updated on: 2026-03-18

Assigner: Mattermost, Inc.

Description
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
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Meta Information
Published
2026-03-16
Last Modified
2026-03-18
Generated
2026-06-16
AI Q&A
2026-03-16
EPSS Evaluated
2026-06-15
NVD
CVE-2026-2455
EUVD
EUVD-2026-12441
Affected Vendors & Products
Showing 3 associated CPEs
Vendor Product Version / Range
mattermost mattermost_server From 10.11.0 (inc) to 10.11.11 (exc)
mattermost mattermost_server From 11.2.0 (inc) to 11.2.3 (exc)
mattermost mattermost_server From 11.3.0 (inc) to 11.3.1 (exc)
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Exploitability
CWE
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KEV
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CWE ID Description
CWE-918 The web server receives a URL or similar request from an upstream component and retrieves the contents of this URL, but it does not sufficiently ensure that the request is being sent to the expected destination.
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Executive Summary

This vulnerability exists in certain versions of Mattermost (11.3.x <= 11.3.0, 11.2.x <= 11.2.2, and 10.11.x <= 10.11.10) where the software fails to properly canonicalize IPv4-mapped IPv6 addresses before performing reserved IP validation.

Because of this failure, an attacker can exploit the system by using IPv4-mapped IPv6 literals (for example, [::ffff:127.0.0.1]) to bypass IP address checks and perform Server-Side Request Forgery (SSRF) attacks against internal services.

Impact Analysis

This vulnerability can allow an attacker with limited privileges to perform SSRF attacks, potentially accessing internal services that are not intended to be exposed externally.

Such SSRF attacks could lead to unauthorized access to internal resources, information disclosure, or further exploitation within the internal network.

The CVSS score of 4.3 indicates a low to medium severity impact, with limited confidentiality impact and no impact on integrity or availability.

Compliance Impact

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