CVE-2026-18551— Mattermost guest account privilege escalation via member roles API
Quick assessment
Affected
Mattermost Mattermost
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.
Mattermost 版本 11.10.x（≤ 11.10.0）、11.7.x（≤ 11.7.9）、11.9.x（≤ 11.9.1）以及 11.8.x（≤ 11.8.5）未能正确验证“访客（guest）”与“管理员（admin）”方案角色的组合，这使得已认证的攻击者能够通过精心构造的 PUT 请求发送至成员角色（member roles）API 端点，将访客账户提升为团队或频道管理员。Mattermost 安全公告编号：MMSA-2026-00752。
Possible ATT&CK Techniques 1 AI
T1548.001 · Setuid and SetgidAffected Version Matrix 9
| Vendor | Product | Version Range | Status |
|---|---|---|---|
| Mattermost | Mattermost | 11.10.0≤ 11.10.0 |
affected |
11.7.0≤ 11.7.9 |
affected | ||
11.9.0≤ 11.9.1 |
affected | ||
11.8.0≤ 11.8.5 |
affected | ||
11.11.0 |
unaffected | ||
11.10.1 |
unaffected | ||
11.7.10 |
unaffected | ||
11.9.2 |
unaffected | ||
| … +1 more rows | |||
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I. Basic Information for CVE-2026-18551
Vulnerability Information
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Vulnerability Title
Mattermost guest account privilege escalation via member roles API
Source: CVE Program / CVE List V5
Vulnerability 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 validate the combination of guest and admin scheme roles which allows an authenticated attacker to escalate a guest account to team or channel admin via a crafted PUT request to the member roles API endpoint.. Mattermost Advisory ID: MMSA-2026-00752
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
授权机制不正确
Source: CVE Program / CVE List V5
Affected Products
| Vendor | Product | Affected Versions | CPE | Subscribe |
|---|---|---|---|---|
| Mattermost | Mattermost | 11.10.0 ~ 11.10.0 | - |
|
II. Public POCs for CVE-2026-18551
| # | POC Description | Source Link | Shenlong Link |
|---|
AI-Generated POC
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Same Patch Batch · Mattermost · 2026-10-16 · 15 CVEs total
| CVE-2026-16453 | 7.1 HIGH | Mattermost SAML RelayState forgery allows unauthorized team membership |
| CVE-2026-19541 | 6.5 MEDIUM | Outgoing OAuth connection client secret exposure during connection validation |
| CVE-2026-19621 | 6.5 MEDIUM | Mattermost leaks interactive-message integration secrets to non-admin users via post-delet |
| CVE-2026-16251 | 6.5 MEDIUM | Mattermost local image proxy allows server memory exhaustion via unbounded image response |
| CVE-2026-18795 | 6.4 MEDIUM | Missing server side validation allowed user to quarantine a DM and GM post |
| CVE-2026-18223 | 5.0 MEDIUM | Mattermost invitation tokens not bound to invited email address allowing unauthorized team |
| CVE-2026-19601 | 4.9 MEDIUM | Disclosure of AD/LDAP bind password via Test Connection |
| CVE-2026-19600 | 4.5 MEDIUM | Mattermost logs plaintext authentication tokens in debug-level server logs on failed auth |
| CVE-2026-19076 | 4.4 MEDIUM | Mattermost fails to reject OAuth application sessions in account type switch, allowing acc |
| CVE-2026-19603 | 4.3 MEDIUM | Private channel ID disclosure via user status endpoints |
| CVE-2026-19867 | 4.3 MEDIUM | Uncapped mention keys in user notification properties allow CPU exhaustion during post pro |
| CVE-2026-18560 | 4.3 MEDIUM | Improper order of authorisations in Mattermost GetFile API leads to an authenticated user |
| CVE-2026-18256 | 4.3 MEDIUM | Private team metadata disclosure via the team search API |
| CVE-2026-18799 | 4.3 MEDIUM | Mattermost Server fails to restrict Slack import account binding, allowing team admins to |
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CVE-2026-18799
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CVE-2026-16251
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Mattermost invitation tokens not bound to invited email addr -
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CVE-2026-18799
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Same weakness: CWE-863
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