EUVD-2026-12407
GHSA-ph22-fw5m-w2q9
Severity by source
AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N
Primary rating from NVD.
CVSS VectorNVD
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N
Lifecycle Timeline
4DescriptionCVE.org
Mattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 fail to sanitize client-supplied post metadata which allows an authenticated attacker to spoof permalink embeds impersonating other users via crafted PUT requests to the post update API endpoint.. Mattermost Advisory ID: MMSA-2025-00569
AnalysisAI
Mattermost fails to properly sanitize client-supplied post metadata in its post update API endpoint, allowing authenticated attackers to spoof permalink embeds and impersonate other users through crafted PUT requests. The vulnerability affects Mattermost versions 11.3.0 and earlier, 11.2.2 and earlier, and 10.11.10 and earlier. While the CVSS score of 4.3 is moderate and requires authentication, the integrity impact allows attackers to deceive users by falsely attributing messages to legitimate users, potentially facilitating social engineering or misinformation campaigns within Mattermost instances.
Technical ContextAI
The vulnerability exists in Mattermost's post metadata handling during PUT requests to the post update API endpoint. The root cause is classified under CWE-346 (Origin Validation Error), indicating the application fails to properly validate and sanitize user-supplied metadata that constructs permalink embeds. These embeds typically display author information, timestamps, and message content; when metadata is not sanitized, an attacker can inject malicious metadata through API calls to modify how embeds are rendered, causing the UI to display false authorship. This is a server-side validation failure rather than client-side rendering issue, meaning the spoofed metadata is stored and served to all users viewing the post. Affected CPE identifiers include cpe:2.3:a:mattermost:mattermost_server for the specified version ranges.
RemediationAI
Immediately upgrade Mattermost Server to version 11.3.1 or later (11.3.x branch), 11.2.3 or later (11.2.x branch), or 10.11.11 or later (10.11.x branch), depending on your current version. Refer to the official Mattermost security advisory MMSA-2025-00569 and vendor release notes for detailed patching instructions. As an interim compensating control pending patching, restrict API access to post update endpoints (PUT /api/v4/posts/{post_id}) through network-level access controls, firewall rules, or reverse proxy policies to limit exposure to trusted internal networks only. Additionally, enable and monitor audit logging for post modification events to detect suspicious metadata changes, and educate users about the risk of message impersonation to reduce social engineering impact.
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Same weakness CWE-346 – Origin Validation Error
View allSame technique Information Disclosure
View allVendor StatusVendor
SUSE
Severity: Medium| Product | Status |
|---|---|
| openSUSE Leap 15.6 | Fixed |
| SUSE Linux Enterprise Module for Package Hub 15 SP5 | Fixed |
| SUSE Linux Enterprise Module for Package Hub 15 SP6 | Fixed |
| openSUSE Leap 15.5 | Fixed |
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External POC / Exploit Code
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