CVE-2026-19867— Uncapped mention keys in user notification properties allow CPU exhaustion during post processing
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）、11.9.x（≤ 11.9.1）、11.8.x（≤ 11.8.5）和 11.7.x（≤ 11.7.10）存在安全漏洞：这些版本未能限制用户通知属性中存储的提及键（mention keys）的数量和大小，也未能对每条帖子执行的二次复杂度多字节关键词匹配进行约束。该漏洞使得已认证用户能够通过在其个人资料中存储过大的 列表，来降低帖子处理性能并消耗其他共享频道的成员的 CPU 资源。Mattermost 安全公告编号：MMSA-2026-00773。
Possible ATT&CK Techniques 2 AI
T1499 · Endpoint Denial of Service T1499.003 · Application Exhaustion FloodAffected Version Matrix 9
| Vendor | Product | Version Range | Status |
|---|---|---|---|
| Mattermost | Mattermost | 11.10.0≤ 11.10.0 |
affected |
11.9.0≤ 11.9.1 |
affected | ||
11.8.0≤ 11.8.5 |
affected | ||
11.7.0≤ 11.7.10 |
affected | ||
11.11.0 |
unaffected | ||
11.10.1 |
unaffected | ||
11.9.2 |
unaffected | ||
11.8.6 |
unaffected | ||
| … +1 more rows | |||
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I. Basic Information for CVE-2026-19867
Vulnerability Information
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Vulnerability Title
Uncapped mention keys in user notification properties allow CPU exhaustion during post processing
Source: CVE Program / CVE List V5
Vulnerability Description
Mattermost versions 11.10.x <= 11.10.0, 11.9.x <= 11.9.1, 11.8.x <= 11.8.5, 11.7.x <= 11.7.10 fail to cap the number and size of mention keys stored in a user's notification properties, and to bound the quadratic multibyte-keyword matching performed for each post, which allows an authenticated user to degrade post-processing latency and consume excessive CPU on behalf of other members of any channel they share via storing an oversized notify_props.mention_keys list on their own profile.. Mattermost Advisory ID: MMSA-2026-00773
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:L
Source: CVE Program / CVE List V5
Vulnerability Type
不加限制或调节的资源分配
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-2026-19867
| # | POC Description | Source Link | Shenlong Link |
|---|
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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-2026-18551 | 6.5 MEDIUM | Mattermost guest account privilege escalation via member roles API |
| 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-2026-18560 | 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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