CVE-2026-4646

Q: How do I fix CVE-2026-4646?

Upgrade mattermost server to 11.5.4 or later.

Q: Is CVE-2026-4646 being actively exploited?

Not that we know of. CVE-2026-4646 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 0.25% is the estimated probability that it will be exploited in the next 30 days. That is higher than 16% of all scored CVEs.

Q: How severe is CVE-2026-4646?

CVE-2026-4646 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-2026-4646 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 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to validate user-supplied input in API request handlers which allows an authenticated attacker to crash the plugin process via a crafted HTTP request to the PR details endpoint.. Mattermost Advisory ID: MMSA-2026-00638

CWE-1287Improper Validation of Specified Type of Input

How to fix

Remediation Available

mattermost serverNVD

Affected:>= 11.5.0, < 11.5.4Fixed in:11.5.4CVE-2026-4646derived from NVD

Affected:>= 10.11.0, < 10.11.15Fixed in:10.11.15CVE-2026-4646derived from NVD

Affected:>= 11.6.0, < 11.6.1Fixed in:11.6.1CVE-2026-4646derived from NVD

Affected:>= 11.4.0, < 11.4.5Fixed in:11.4.5CVE-2026-4646derived 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

0.25%probability of exploitation in 30 days

16thpercentile

Low risk: more likely to be exploited than 16% of all known CVEs.

References

Vendor Advisory1

mattermost.com

Related Vulnerabilities

Other CWE-1287 (Improper Validation of Specified Type of Input) vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2024-4879	Critical	9.8	100%	KEV	-
CVE-2022-31007	Medium	4.9	27%	-	Fix
CVE-2024-6298	Critical	10.0	19%	-	-
CVE-2026-25639	High	7.5	2.7%	-	Fix
CVE-2021-43802	Critical	9.9	2.0%	-	Fix
CVE-2026-5946	High	7.5	1.9%	-	Fix

Common questions

How do I fix CVE-2026-4646?

Upgrade mattermost server to 11.5.4 or later.

Is CVE-2026-4646 being actively exploited?

Not that we know of. CVE-2026-4646 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 0.25% is the estimated probability that it will be exploited in the next 30 days. That is higher than 16% of all scored CVEs.

How severe is CVE-2026-4646?

CVE-2026-4646 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-2026-4646 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.

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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 2026-07-23.