Is CVE-2025-21088 in the CISA KEV catalog?

No. CVE-2025-21088 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2025-21088?

CVE-2025-21088 has a CVSS v3 base score of 6.5 (MEDIUM).

What is the EPSS score for CVE-2025-21088?

CVE-2025-21088 has an EPSS score of 0.54% (41th percentile), estimating the probability of exploitation in the next 30 days.

How do I fix CVE-2025-21088?

Upgrade mattermost server to 10.1.4 or later.

CVE & CISA-KEV Catalog

CVE-2025-21088

MEDIUM

6.5

CVSS v3

NVD

Description

Mattermost versions 10.2.x <= 10.2.0, 9.11.x <= 9.11.5, 10.0.x <= 10.0.3, 10.1.x <= 10.1.3 fail to properly validate the style of proto supplied to an action's style in post.props.attachments, which allows an attacker to crash the frontend via crafted malicious input.

CWE-704

How to fix

Remediation Available

mattermost serverNVD

Affected:>= 10.1.0, < 10.1.4Fixed in:10.1.4CVE-2025-21088derived from NVD

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

AvailabilityHigh

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

Exploit Intelligence

0.54%probability of exploitation in 30 days

41stpercentile

Moderate risk: more likely to be exploited than 41% of all known CVEs.

References

Vendor Advisory1

mattermost.com

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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 2025-09-30.