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CVE-2026-19867

Uncapped mention keys in user notification properties allow CPU exhaustion during post processing

Medium4.3EPSS 0.22%
Published
Updated
Reserved
Assigned by
Mattermost

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

Timeline

  1. ID reserved

    By Mattermost

  2. · 2 months later

    Published

Changes after publication (a new score, a public exploit, EPSS crossing 1, 10 or 50 %, leaving KEV) are kept since November 2026; earlier ones are not known.

Scores

CVSS scores of CVE-2026-19867, by who scored it
Scored byCVSSScoreVector
MattermostCNA (assigner)3.1Medium4.3CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
NVDNVD · Analyzed3.1Medium4.3CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
EPSS (exploitation in 30 days)
0.22% · top 88% of all CVEs (7 Nov 2026)
CISA SSVC
Exploitation: none · Automatable: no · Technical impact: partial
Loading the EPSS history…

The list uses the assigner's score when there is one, then CISA's, then NVD's: Medium 4.3.

Weakness

Affected products

  • Mattermost · Mattermost

    • affected 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
    • unaffected 11.11.0
    • unaffected 11.10.1
    • unaffected 11.9.2
    • unaffected 11.8.6
    • unaffected 11.7.11

What to do

Solution: Update Mattermost to versions 11.11.0, 11.10.1, 11.9.2, 11.8.6, 11.7.11 or higher.

References (1)

Sources

The same CVE in the primary databases and aggregators, to check against.

Badge for a README or a ticket

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Record last updated .