Is CVE-2026-6333 in the CISA KEV catalog?

No. CVE-2026-6333 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2026-6333?

CVE-2026-6333 has a CVSS v3 base score of 3.5 (LOW).

What is the EPSS score for CVE-2026-6333?

CVE-2026-6333 has an EPSS score of 0.14% (3th percentile), estimating the probability of exploitation in the next 30 days.

How do I fix CVE-2026-6333?

Upgrade mattermost server to 11.5.2 or later.

CVE & CISA-KEV Catalog

CVE-2026-6333

LOW

3.5

CVSS v3

NVD

Description

Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13 fail to validate the Host header when constructing response URLs for custom slash commands which allows an authenticated attacker to redirect slash command responses to an attacker-controlled server via a spoofed Host header.. Mattermost Advisory ID: MMSA-2026-00582

CWE-918Server-Side Request Forgery (SSRF)

How to fix

Remediation Available

mattermost serverNVD

Affected:>= 11.5.0, < 11.5.2Fixed in:11.5.2CVE-2026-6333derived 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 ComplexityHigh

Privileges RequiredLow

User InteractionNone

ScopeChanged

Impact

ConfidentialityNone

IntegrityLow

AvailabilityNone

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

Exploit Intelligence

0.14%probability of exploitation in 30 days

3rdpercentile

Low risk: more likely to be exploited than 3% of all known CVEs.

References

Vendor Advisory1

mattermost.com

Related Vulnerabilities

Other CWE-918 (Server-Side Request Forgery (SSRF)) vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2024-21893	High	8.2	100%	KEV + Ransom	-
CVE-2021-40438	Critical	9.0	100%	KEV	Fix
CVE-2021-34473	Critical	9.1	100%	KEV + Ransom	Fix
CVE-2021-26855	Critical	9.1	100%	KEV + Ransom	Fix
CVE-2021-21985	Critical	9.8	100%	KEV + Ransom	Fix
CVE-2022-41040	High	8.8	100%	KEV + Ransom	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 2026-05-19.