How severe is CVE-2026-2456?

CVE-2026-2456 has a CVSS 3.x base score of 5.3, rated medium severity. It is exploitable over network with high attack complexity, requires no privileges and user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2026-2456 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (6th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-2456?

CVE-2026-2456 affects Mattermost Mattermost Server. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-2456?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

Does CVE-2026-2456 have an EU (EUVD) identifier?

Yes. CVE-2026-2456 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-12383.

When was CVE-2026-2456 published?

CVE-2026-2456 was published on 2026-03-16 and last updated on 2026-06-17.

CVE-2026-2456

CVE-2026-2456 is a medium-severity vulnerability in Mattermost Mattermost Server with a CVSS 3.x base score of 5.3. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-789.

Key facts

Severity: Medium (CVSS 3.x base score 5.3)
EPSS exploit prediction: 0% (6th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-12383
Weakness: CWE-789
Affected product: Mattermost Mattermost Server
Published: 2026-03-16
Last modified: 2026-06-17

Description

Mattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 Mattermost fails to limit the size of responses from integration action endpoints, which allows an authenticated attacker to cause server memory exhaustion and denial of service via a malicious integration server that returns an arbitrarily large response when a user clicks an interactive message button.. Mattermost Advisory ID: MMSA-2026-00571

Frequently asked questions

What is CVE-2026-2456?: Mattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 Mattermost fails to limit the size of responses from integration action endpoints, which allows an authenticated attacker to cause server memory exhaustion and denial of service via a malicious integration server that returns an arbitrarily large response when a user clicks an interactive message button.. Mattermost Advisory ID: MMSA-2026-00571
How severe is CVE-2026-2456?: CVE-2026-2456 has a CVSS 3.x base score of 5.3, rated medium severity. It is exploitable over network with high attack complexity, requires no privileges and user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2026-2456 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (6th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-2456?: CVE-2026-2456 affects Mattermost Mattermost Server. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-2456?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2026-2456 have an EU (EUVD) identifier?: Yes. CVE-2026-2456 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-12383.
When was CVE-2026-2456 published?: CVE-2026-2456 was published on 2026-03-16 and last updated on 2026-06-17.

References

https://mattermost.com/security-updates

Affected products (1)

cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*

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