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CVE-2026-2325· NVD / CVE Program· CNA Mattermost

Improper Input Validation in MS Teams Meetings API Handler

Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13, 11.4.x <= 11.4.3 fail to limit the size of the request body on the start meeting API endpoint, which allows an authenticated attacker to cause resource exhaustion or denial of service via a crafted oversized HTTP POST request to {{/api/v1/meetings}}.. Mattermost Advisory ID: MMSA-2026-00608

MediumCVSS 6.5 · v3.1—No exploit Fix available

Noroxi analysis

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Published
May 18, 2026
Updated
Jun 17, 2026
EPSS
0.2% · 14th percentile
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Report tools

JSON

Action score

26

Monitor

Low priority for now.

CVSS
26 / 40 · 6.5 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.2%

CISA SSVC decision

Exploitation
none
Automatable
no
Technical impact
partial

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD
6.5
CNA · Mattermost
4.3
2.2 point gap

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

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Affected systems

VendorProduct
mattermostmattermost server

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • mattermost mattermost server10.11.0 and later · before 10.11.14
  • mattermost mattermost server11.4.0 and later · before 11.4.4
  • mattermost mattermost server11.5.0 and later · before 11.5.2

Versions reported by the vendor

Affected version ranges reported by the assigning authority (Mattermost). Independent of NVD's CPE analysis and usually ahead of it.

  • Mattermost Mattermost

    • 11.6.0, 11.5.2, 10.11.14, 11.4.4not affected
    • 11.5.0 and later · up to and including 11.5.1affected · semver
    • 10.11.0 and later · up to and including 10.11.13affected · semver
    • 11.4.0 and later · up to and including 11.4.3affected · semver

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
Gogithub.com/mattermost/mattermost-plugin-msteams-meetingsbefore 1.1.1-0.20260213105619-c5892dd169de1.1.1-0.20260213105619-c5892dd169de
Gogithub.com/mattermost/mattermost-serverfrom 10.11.0 · before 10.11.1410.11.14
Gogithub.com/mattermost/mattermost-serverfrom 10.11.0+incompatible · before 10.11.14+incompatible10.11.14+incompatible
Gogithub.com/mattermost/mattermost-serverfrom 11.4.0 · before 11.4.411.4.4
Gogithub.com/mattermost/mattermost-serverfrom 11.4.0+incompatible · before 11.4.4+incompatible11.4.4+incompatible
Gogithub.com/mattermost/mattermost-serverfrom 11.5.0 · before 11.5.211.5.2
Gogithub.com/mattermost/mattermost-serverfrom 11.5.0+incompatible · before 11.5.2+incompatible11.5.2+incompatible

Same product

mattermost: all records

Other highest-scoring records for the same primary product.

  • CVE-2026-4858Path traversal in integration action URL leading to arbitrary API execution via system admin’s auth token.
    39Monitor
  • CVE-2025-12421Account Takeover via Code Exchange Endpoint
    39Monitor
  • CVE-2025-12419Account takeover on OAuth/OpenID-enabled servers
    39Monitor
  • CVE-2025-4981Path Traversal Leading to RCE by Any Authenticated Mattermost User
    39Monitor
  • CVE-2023-6458Client side path traversal due to lack of route parameters validation
    39Monitor
  • CVE-2017-18920An issue was discovered in Mattermost Server before 3.6.2.
    39Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
Go:github.com/mattermost/mattermost-plugin-msteams-meetings1.1.1-0.20260213105619-c5892dd169dePackage registry (OSV)
Go:github.com/mattermost/mattermost-server10.11.14Package registry (OSV)
Go:github.com/mattermost/mattermost-server10.11.14+incompatiblePackage registry (OSV)
Go:github.com/mattermost/mattermost-server11.4.4Package registry (OSV)
Go:github.com/mattermost/mattermost-server11.4.4+incompatiblePackage registry (OSV)
Go:github.com/mattermost/mattermost-server11.5.2Package registry (OSV)
Go:github.com/mattermost/mattermost-server11.5.2+incompatiblePackage registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

EPSS, last 120 days

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

  • CVE-2026-2445863 days apartDoS attack via login attempts with multi-megabyte passwords
    30Monitor
  • CVE-2025-35965389 days apartDoS in Mattermost Playbooks via Excessive Task Actions
    30Monitor
  • CVE-2026-2138839 days apartUnbounded Request Body Read in MS Teams Plugin {{/lifecycle}} Webhook Endpoint
    26Monitor
  • CVE-2025-14435122 days apartApplication-Level DoS via infinite re-render loop in user profile handling
    26Monitor
  • CVE-2026-1060070 days apartDenial of service via unbounded document content extraction in Mattermost Server
    17Monitor

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

The product’s vendor appears in a public program. Matched by name; verify the scope text in the program.

Technical details

Attack conditions

  • Anyone who can reach it over the internet can trigger it.
  • A low-privileged account is enough.
  • No user action is required.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
none
Integrity
none
Availability
high · the service can be disrupted
Attack vector
Network
Attack complexity
Low
Privileges required
Low
User interaction
None
Scope
Unchanged
Confidentiality impact
None
Integrity impact
None
Availability impact
High

Weakness class (CWE)

CWE-770 · Allocation of Resources Without Limits or Throttling

CVSS vector

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

nvd-primary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

Change log

  1. Fix✗ → ✓

For records you follow, these changes also arrive as notifications. →

References

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records