How severe is CVE-2026-25783?

CVE-2026-25783 has a CVSS 3.x base score of 4.3, rated medium severity. It is exploitable over network with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability low.

Is CVE-2026-25783 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (20th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-25783?

CVE-2026-25783 affects Mattermost Mattermost Server. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-25783?

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

Does CVE-2026-25783 have an EU (EUVD) identifier?

Yes. CVE-2026-25783 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-12416.

When was CVE-2026-25783 published?

CVE-2026-25783 was published on 2026-03-16 and last updated on 2026-06-17.

CVE-2026-25783

CVE-2026-25783 is a medium-severity vulnerability in Mattermost Mattermost Server with a CVSS 3.x base score of 4.3. 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-1287.

Key facts

Severity: Medium (CVSS 3.x base score 4.3)
EPSS exploit prediction: 0% (20th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-12416
Weakness: CWE-1287
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 fail to properly validate User-Agent header tokens which allows an authenticated attacker to cause a request panic via a specially crafted User-Agent header. Mattermost Advisory ID: MMSA-2026-00586

Frequently asked questions

What is CVE-2026-25783?: Mattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 fail to properly validate User-Agent header tokens which allows an authenticated attacker to cause a request panic via a specially crafted User-Agent header. Mattermost Advisory ID: MMSA-2026-00586
How severe is CVE-2026-25783?: CVE-2026-25783 has a CVSS 3.x base score of 4.3, rated medium severity. It is exploitable over network with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability low.
Is CVE-2026-25783 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (20th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-25783?: CVE-2026-25783 affects Mattermost Mattermost Server. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-25783?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2026-25783 have an EU (EUVD) identifier?: Yes. CVE-2026-25783 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-12416.
When was CVE-2026-25783 published?: CVE-2026-25783 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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