CVE-2026-6850— Crafted message attachment causes client-side denial of service via markdown parser regex backtracking in Mattermost
Possible ATT&CK Techniques 1AI
T1499 · Endpoint Denial of ServiceAffected Version Matrix 7
| Vendor | Product | Version Range | Status |
|---|---|---|---|
| Mattermost | Mattermost | 11.7.0≤ 11.7.2 | affected |
11.6.0≤ 11.6.4 | affected | ||
10.11.0≤ 10.11.19 | affected | ||
11.8.0 | unaffected | ||
11.7.3 | unaffected | ||
11.6.5 | unaffected | ||
10.11.20 | unaffected |
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I. Basic Information for CVE-2026-6850
Vulnerability Information
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Vulnerability Title
Crafted message attachment causes client-side denial of service via markdown parser regex backtracking in Mattermost
Source: CVE Program / CVE List V5
Vulnerability Description
Mattermost versions 11.7.x <= 11.7.2, 11.6.x <= 11.6.4, 10.11.x <= 10.11.19 fail to validate the length and content of message attachment field values, which allows an authenticated attacker to cause a denial of service for all users in a channel via a post containing a specially crafted payload that triggers catastrophic backtracking in the client-side markdown parser.. Mattermost Advisory ID: MMSA-2026-00658
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
CWE-1333
Source: CVE Program / CVE List V5
Vulnerability Title
Mattermost 资源管理错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Mattermost是美国Mattermost公司开源的一个开源协作平台。 Mattermost存在资源管理错误漏洞，该漏洞源于未能验证消息附件字段值的长度和内容，使得经过身份认证的攻击者可以通过发布包含特制有效载荷的帖子触发客户端markdown解析器的灾难性回溯，导致频道内所有用户遭受拒绝服务攻击。以下版本受到影响：10.11.19及之前的10.11.x版本、11.6.4及之前的11.6.x版本和11.7.2及之前的11.7.x版本。
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 | 11.7.0 ~ 11.7.2 | - |
II. Public POCs for CVE-2026-6850
| # | POC Description | Source Link | Shenlong Link |
|---|
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Same Patch Batch · Mattermost · 2026-07-13 · 10 CVEs total
| CVE-2026-10106 | 6.5 MEDIUM | Unauthorized users can trigger interactive post actions in private channels via action coo |
| CVE-2026-9571 | 5.9 MEDIUM | Deactivated user accounts can continue to obtain valid OAuth access tokens via refresh tok |
| CVE-2026-9597 | 5.4 MEDIUM | Deactivated guest accounts can authenticate via magic-link token in Mattermost REST API lo |
| CVE-2026-10085 | 5.4 MEDIUM | Ordinary group/direct message member can enable group_constrained and remove all channel p |
| CVE-2026-9708 | 4.9 MEDIUM | Incoming webhook user attribution via unvalidated webhook owner |
| CVE-2026-6541 | 4.3 MEDIUM | Unscoped updates to other playbooks' metric configuration |
| CVE-2026-9824 | 4.3 MEDIUM | Remote cluster metadata enumeration via /share-channel autocomplete |
| CVE-2026-10103 | 4.3 MEDIUM | Authenticated remote cluster can modify or delete posts it does not own in Mattermost Conn |
| CVE-2026-9820 | 3.8 LOW | Mattermost schemes teams endpoint exposes private team invite IDs |
IV. Related Vulnerabilities
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Same vendor: Mattermost
- CVE-2026-75587
Plaintext pre-auth secret exposure via Desktop App diagnosti - CVE-2026-9693
Mattermost thread memberships persist after team removal, ex - CVE-2026-9859
Mattermost Boards plugin didn’t enforce role-based authoriza - CVE-2026-9816
Insufficient server-side validation of board member role fie - CVE-2026-10080
Boards plugin panics on WebSocket command with non-string fi
Same weakness: CWE-1333
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