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VulnerabilityPublished

CVE-2026-19867: Mattermost · Unthrottled Resource Allocation

Affects MattermostSource GCVE Database

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Not known to be exploited · CVSS 4.3 Medium.

Data as of 29 Oct 2026, 22:00 UTC

CVSS 3.1 base score
4.3Medium
How severe the flaw is on the 0–10 CVSS scale.

Thin evidence

One scorer or none
CVSS scores by source
CNA (Mattermost)CVSS 3.14.3
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 16 Oct 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq 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

ProductAffectedFixed in
Mattermost MattermostAffected
  • 11.7.0 – 11.10.0
4 affected builds
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.

References

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