Is CVE-2026-4265 in the CISA KEV catalog?

No. CVE-2026-4265 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2026-4265?

CVE-2026-4265 has a CVSS v3 base score of 4.3 (MEDIUM).

What is the EPSS score for CVE-2026-4265?

CVE-2026-4265 has an EPSS score of 0.22% (12th percentile), estimating the probability of exploitation in the next 30 days.

How do I fix CVE-2026-4265?

Upgrade mattermost server to 11.3.1 or later.

CVE & CISA-KEV Catalog

CVE-2026-4265

MEDIUM

4.3

CVSS v3

NVD

Description

Mattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 fail to validate team-specific upload_file permissions which allows a guest user to post files in channels where they lack upload_file permission via uploading files in a team where they have permission and reusing the file metadata in a POST request to a different team. Mattermost Advisory ID: MMSA-2025-00553

CWE-863Incorrect Authorization

How to fix

Remediation Available

mattermost serverNVD

Affected:>= 11.3.0, < 11.3.1Fixed in:11.3.1CVE-2026-4265derived 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

IntegrityLow

AvailabilityNone

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

Exploit Intelligence

0.22%probability of exploitation in 30 days

12thpercentile

Low risk: more likely to be exploited than 12% of all known CVEs.

References

Vendor Advisory1

mattermost.com

Related Vulnerabilities

Other CWE-863 (Incorrect Authorization) vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2023-22518	Critical	9.8	100%	KEV + Ransom	Fix
CVE-2023-38035	Critical	9.8	100%	KEV + Ransom	-
CVE-2022-46169	Critical	9.8	100%	KEV	Fix
CVE-2025-29927	Critical	9.1	100%	-	Fix
CVE-2024-38856	Critical	9.8	99%	KEV	Fix
CVE-2020-36289	Medium	5.3	99%	-	Fix

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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 2026-03-18.