What is the CVSS score of CVE-2026-25783?

CVE-2026-25783 has a CVSS 3.1 base score of 4.3 (Medium). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L. EPSS exploitation probability: 0.1%.

Which versions of Mattermost are affected by CVE-2026-25783?

CVE-2026-25783 presents moderate security risk rated CVSS 4.3. Exploitation could compromise the security of affected deployments.. A patch is available.

How to fix or mitigate CVE-2026-25783?

Within 30 days: Identify affected systems and apply vendor patches as part of regular patch cycle. Monitor vendor channels for patch availability.

Mattermost CVE-2026-25783

EUVD-2026-12416 MEDIUM

Improper Validation of Specified Type of Input (CWE-1287)

2026-03-16 Mattermost

GHSA-2v3w-6g35-5f9v

Information Disclosure Mattermost Suse

4.3

CVSS 3.1 · NVD

Severity by source

NVD PRIMARY

4.3 MEDIUM

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

SUSE

MEDIUM

qualitative

Primary rating from NVD.

CVSS VectorNVD

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

Attack Vector

Network

Attack Complexity

Low

Privileges Required

Low

User Interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

None

Availability

Low

Lifecycle Timeline

Patch released

Mar 31, 2026 - 21:13 nvd

Patch available

EUVD ID Assigned

Mar 16, 2026 - 13:00 euvd

EUVD-2026-12416

Analysis Generated

Mar 16, 2026 - 13:00 vuln.today

CVE Published

Mar 16, 2026 - 12:04 nvd

MEDIUM 4.3

DescriptionCVE.org

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

AnalysisAI

Mattermost fails to properly validate User-Agent header tokens in versions 11.3.0 and earlier, 11.2.2 and earlier, and 10.11.10 and earlier, allowing authenticated attackers to trigger request panics through specially crafted User-Agent headers. This denial-of-service vulnerability affects availability but requires prior authentication and results in only low-severity impact. While the CVSS score of 4.3 reflects the low severity, the practical risk depends on whether the application is exposed to untrusted authenticated users and whether automatic exploitation tools are readily available.

Technical ContextAI

The vulnerability resides in Mattermost's HTTP request handling layer, specifically in the User-Agent header parsing and validation mechanism. Under CWE-1287 (Improper Validation of Specified Quantity in Input), the application fails to implement robust bounds checking or format validation on the User-Agent header token before processing it. This likely manifests as a null pointer dereference, buffer overflow, or uncaught exception when the crafted header is processed, causing the request handler to panic and crash. The affected technology is Mattermost's core server component (cpe:2.3:a:mattermost:mattermost_server) versions spanning 10.11.x through 11.3.x, which handle HTTP request parsing as part of the collaborative messaging platform's request processing pipeline.

RemediationAI

Upgrade Mattermost Server to version 11.3.1 or later for 11.3.x deployments, version 11.2.3 or later for 11.2.x deployments, and version 10.11.11 or later for 10.11.x deployments. Consult the official Mattermost advisory (MMSA-2026-00586) and security update page at https://mattermost.com/security-updates/ for patch availability and detailed instructions. As interim mitigations before patching is feasible, implement rate limiting on HTTP requests with malformed or oversized User-Agent headers at the reverse proxy layer, restrict Mattermost access to authenticated users from known IP ranges, and configure monitoring alerts to detect request panic events in application logs. Consider deploying a Web Application Firewall (WAF) to sanitize inbound User-Agent headers.

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Vendor StatusVendor

SUSE

Severity: Medium

Product	Status
openSUSE Leap 15.6	Fixed
SUSE Linux Enterprise Module for Package Hub 15 SP5	Fixed
SUSE Linux Enterprise Module for Package Hub 15 SP6	Fixed
openSUSE Leap 15.5	Fixed

CVE-2026-25783 vulnerability details – vuln.today

Back

Mattermost CVE-2026-25783

Severity by source

CVSS VectorNVD

Lifecycle Timeline

DescriptionCVE.org

AnalysisAI

Technical ContextAI

RemediationAI

More in Mattermost

Same weakness CWE-1287 – Improper Validation of Specified Type of Input

Same technique Information Disclosure

Vendor StatusVendor

SUSE

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External POC / Exploit Code