CVE-2026-86349

Q: How do I fix CVE-2026-86349?

Upgrade mattermost server to 11.9.1 or later.

Q: Is CVE-2026-86349 being actively exploited?

Not that we know of. CVE-2026-86349 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 0.37% is the estimated probability that it will be exploited in the next 30 days. That is higher than 29% of all scored CVEs.

Q: How severe is CVE-2026-86349?

CVE-2026-86349 has a CVSS v3 base score of 4.3, rated medium. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.

Q: What does CVE-2026-86349 affect?

Published advisories record a fix for mattermost server (NVD). Only products with a sourced advisory are listed, so treat this as what we can cite rather than a complete inventory.

MEDIUM

4.3

CVSS v3

NVD

Description

Mattermost versions 11.9.x <= 11.9.0, 11.8.x <= 11.8.4, 11.7.x <= 11.7.8, 10.11.x <= 10.11.22 fail to limit the nesting depth in the server-side Markdown parser which allows an authenticated attacker to cause a denial of service (CPU resource exhaustion) via a crafted post containing deeply nested blockquotes or list items.. Mattermost Advisory ID: MMSA-2026-00707

CWE-407

How to fix

Remediation Available

mattermost serverNVD

Affected:>= 11.9.0, < 11.9.1Fixed in:11.9.1CVE-2026-86349derived from NVD

Affected:>= 11.8.0, < 11.8.5Fixed in:11.8.5CVE-2026-86349derived from NVD

Affected:>= 10.11.0, < 10.11.23Fixed in:10.11.23CVE-2026-86349derived from NVD

Affected:>= 11.7.0, < 11.7.9Fixed in:11.7.9CVE-2026-86349derived from NVD

TridentStack Control can deploy fixes like this automatically across your Windows, macOS, and Linux fleet. See how it works

Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.

CVSS v3 Vector

Exploitability

Attack VectorNetwork

Attack ComplexityLow

Privileges RequiredLow

User InteractionNone

ScopeUnchanged

Impact

ConfidentialityNone

IntegrityNone

AvailabilityLow

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L

Exploit Intelligence

0.37%probability of exploitation in 30 days

29thpercentile

Low risk: more likely to be exploited than 29% of all known CVEs.

References

Vendor Advisory1

mattermost.com

Related Vulnerabilities

Other CWE-407 vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2020-27223	Medium	5.2	78%	-	Fix
CVE-2022-36021	Medium	5.5	60%	-	Fix
CVE-2021-33582	High	7.5	3.1%	-	Fix
CVE-2024-43485	High	7.5	3.1%	-	Fix
CVE-2024-43484	High	7.5	3.0%	-	Fix
CVE-2016-10396	High	7.5	2.9%	-	-

Common questions

How do I fix CVE-2026-86349?

Upgrade mattermost server to 11.9.1 or later.

Is CVE-2026-86349 being actively exploited?

Not that we know of. CVE-2026-86349 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 0.37% is the estimated probability that it will be exploited in the next 30 days. That is higher than 29% of all scored CVEs.

How severe is CVE-2026-86349?

CVE-2026-86349 has a CVSS v3 base score of 4.3, rated medium. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.

What does CVE-2026-86349 affect?

Published advisories record a fix for mattermost server (NVD). Only products with a sourced advisory are listed, so treat this as what we can cite rather than a complete inventory.

Embed a live status badge for CVE-2026-86349

Markdown

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HTML

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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-10-07.