CVE-2026-19867: Mattermost · Unthrottled Resource Allocation
Affects MattermostSource GCVE Database
Not known to be exploited · CVSS 4.3 Medium.
Data as of 29 Oct 2026, 22:00 UTC
Thin evidence
One scorer or none| CNA (Mattermost) | CVSS 3.1 | 4.3 |
|---|
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:LExploitation evidence
Disclosed: evidence found.
CVE published 16 Oct 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors
A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 29 Oct 2026.
What to do
Affected software
| Product | Affected | Fixed in |
|---|---|---|
| Mattermost Mattermost | Affected
| Fixed in– |
AI-suggested
Until a fix is available, consider limiting user input sizes or monitoring for abnormal resource usage related to mention keys. Since this requires authenticated user access, restricting user permissions may reduce risk.
Description
CVE-2026-19867 is a resource allocation vulnerability in Mattermost versions 11.7.0, 11.8.0, 11.9.0, and 11.10.0. It arises because the software does not limit the number or size of mention keys stored in a user's notification properties, nor does it bound the quadratic multibyte-keyword matching during post processing. An authenticated user can exploit this by storing an oversized mention_keys list in their profile, causing excessive CPU consumption and degraded post-processing latency for other channel members.