CVE-2026-21386— Private channel enumeration via /mute slash command
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I. Basic Information for CVE-2026-21386
Vulnerability Information
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Vulnerability Title
Private channel enumeration via /mute slash command
Source: NVD (National Vulnerability Database)
Vulnerability Description
Mattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 fail to use consistent error responses when handling the /mute command which allows an authenticated team member to enumerate private channels they are not authorized to know about via differing error messages for nonexistent versus private channels. Mattermost Advisory ID: MMSA-2026-00588
Source: NVD (National Vulnerability Database)
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
Source: NVD (National Vulnerability Database)
Vulnerability Type
通过差异性导致的信息暴露
Source: NVD (National Vulnerability Database)
Vulnerability Title
Mattermost 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Mattermost是美国Mattermost公司的一个开源协作平台。 Mattermost 11.3.0及之前的11.3.x版本、11.2.2及之前的11.2.x版本和10.11.10及之前的10.11.x版本存在安全漏洞，该漏洞源于处理/mute命令时错误响应不一致，可能导致经过身份验证的团队成员通过不同的错误消息枚举未获授权的私有频道。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)
Affected Products
| Vendor | Product | Affected Versions | CPE | Subscribe |
|---|---|---|---|---|
| Mattermost | Mattermost | 11.3.0 ~ 11.3.0 | - |
II. Public POCs for CVE-2026-21386
| # | POC Description | Source Link | Shenlong Link |
|---|
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Same Patch Batch · Mattermost · 2026-03-16 · 21 CVEs total
| CVE-2026-2476 | 7.6 HIGH | MS Teams plugin sensitive config values not properly masked in support packets |
| CVE-2026-24458 | 7.5 HIGH | DoS attack via login attempts with multi-megabyte passwords |
| CVE-2026-2462 | 6.6 MEDIUM | Admin RCE via Malicious Plugin Upload on CI Test Instances |
| CVE-2026-2454 | 5.8 MEDIUM | DoS in Calls plugin via malformed msgpack in websocket request. |
| CVE-2026-2456 | 5.3 MEDIUM | Denial of Service via Unbounded Memory Allocation in Integration Actions |
| CVE-2026-2455 | 4.3 MEDIUM | SSRF bypass via IPv4-mapped IPv6 literals |
| CVE-2026-25780 | 4.3 MEDIUM | Memory Exhaustion via Malformed DOC File Upload |
| CVE-2026-4265 | 4.3 MEDIUM | Guest user can upload files without permission across teams |
| CVE-2026-25783 | 4.3 MEDIUM | Denial of service via malformed User-Agent header in getBrowserVersion |
| CVE-2026-24692 | 4.3 MEDIUM | Guest users can bypass read permissions via search API |
| CVE-2026-26304 | 4.3 MEDIUM | Permission Bypass in Playbook Run Creation |
| CVE-2026-2578 | 4.3 MEDIUM | Information Disclosure via WebSocket Event When Deleting Unrevealed Burn on Read Posts |
| CVE-2026-26246 | 4.3 MEDIUM | Memory Exhaustion via Malformed PSD File Upload |
| CVE-2026-2458 | 4.3 MEDIUM | Unauthorized channel enumeration in private teams after member removal |
| CVE-2026-2457 | 4.3 MEDIUM | WebSocket Message Spoofing via Permalink Embed Manipulation |
| CVE-2026-2461 | 4.3 MEDIUM | Missing authorization check allows unauthorized modification of other users' comments on a |
| CVE-2026-2463 | 4.3 MEDIUM | Unauthorized access to invite ID during team creation |
| CVE-2026-1629 | 4.3 MEDIUM | Permalink Preview Information Disclosure After Permission Revocation |
| CVE-2026-26230 | 3.8 LOW | Team Admin Privilege Escalation to Demote Members to Guest |
| CVE-2026-22545 | 3.1 LOW | Password Change Bypass via Auth Switch Endpoint |
IV. Related Vulnerabilities
Same product: Mattermost
- CVE-2026-3590
Race Condition in Guest Magic Link Authentication Allows Tok - CVE-2026-28741
CSRF Protection Bypass Allows Updating a User's Authenticati - CVE-2026-27769
Connected Workspaces: Malicious remote server can manipulate - CVE-2026-24661
Unbounded Request Body Read in MS Teams Plugin {{/changes}} - CVE-2026-21388
Unbounded Request Body Read in MS Teams Plugin {{/lifecycle}
Same vendor: Mattermost
- CVE-2026-3590
Race Condition in Guest Magic Link Authentication Allows Tok - CVE-2026-28741
CSRF Protection Bypass Allows Updating a User's Authenticati - CVE-2026-27769
Connected Workspaces: Malicious remote server can manipulate - CVE-2026-24661
Unbounded Request Body Read in MS Teams Plugin {{/changes}} - CVE-2026-21388
Unbounded Request Body Read in MS Teams Plugin {{/lifecycle}
Same weakness: CWE-203
- CVE-2026-44263
Weblate: Private Translation Enumeration via Screenshot API - CVE-2023-5872
Wago: Vulnerability in Smart Designer Web-Application - CVE-2026-33429
Parse Server: Protected field change detection oracle via Li - CVE-2026-33425
Discourse has inferable private group membership or existenc - CVE-2026-3580
Compiler-induced timing leak in sp_256_get_entry_256_9 on RI
V. Comments for CVE-2026-21386
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