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NVD / CVE Program· CNA Mattermost

CVE-2026-4273: Insufficient token rotation validation in remote cluster invite confirmation

Noroxi assessment

Priority: Monitor (action score 17/100)

  • The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
  • Probability of exploitation in the next 30 days: 0.14% (FIRST EPSS).
  • 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.
  • Fixed version: github.com/mattermost/mattermost-server (Go) 10.11.14+incompatible, 11.5.2+incompatible, 5.3.2-0.20260313190740-742e0be95074; github.com/mattermost/mattermost/server/v8 (Go) 10.11.14, 11.5.2, 8.0.0-20260313190740-742e0be95074.

Low priority for now. Upgrade to github.com/mattermost/mattermost-server (Go) 10.11.14+incompatible, 11.5.2+incompatible, 5.3.2-0.20260313190740-742e0be95074; github.com/mattermost/mattermost/server/v8 (Go) 10.11.14, 11.5.2, 8.0.0-20260313190740-742e0be95074 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13 fail to validate that the RefreshedToken differs from the original invite token during remote cluster invite confirmation which allows an authenticated attacker to bypass token rotation and reuse the original invite token via sending a crafted invite confirmation with a RefreshedToken matching the original token. Mattermost Advisory ID: MMSA-2026-00575

MediumCVSS 4.3 · v3.1—No exploit Fix available
Published
May 18, 2026
Updated
Oct 14, 2026
EPSS
0.1% · 3th percentile

Report tools

JSON

Action score

17

Monitor

Low priority for now.

CVSS
17 / 40 · 4.3 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.1%

CISA SSVC decision

Exploitation
none
Automatable
no
Technical impact
partial

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD
4.3
CNA · Mattermost
3.7
0.6 point gap

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

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

Get told when this record changes

  • Not in KEV: no record of exploitation in the wild
  • No public exploit code on record
  • A fix has been released

If any of these changes, we'll tell you in the daily email digest.

Follow CVE-2026-4273

When you'll hear from us

  • when it enters CISA KEV
  • when exploit code appears or is weaponized
  • when the record is updated (including a fixed version)
  • when EPSS rises 20 points in a week

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

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 server11.5.0 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, 10.11.14not 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

Package-level exposure

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

EcosystemPackageAffected rangeFix
Gogithub.com/mattermost/mattermost-serverfrom 10.11.0+incompatible · before 10.11.14+incompatible10.11.14+incompatible
Gogithub.com/mattermost/mattermost-serverfrom 11.5.0+incompatible · before 11.5.2+incompatible11.5.2+incompatible
Gogithub.com/mattermost/mattermost-serverbefore 5.3.2-0.20260313190740-742e0be950745.3.2-0.20260313190740-742e0be95074
Gogithub.com/mattermost/mattermost-server/v5from 0—
Gogithub.com/mattermost/mattermost-server/v6from 0—
Gogithub.com/mattermost/mattermost/server/v8from 10.11.0 · before 10.11.1410.11.14
Gogithub.com/mattermost/mattermost/server/v8from 11.5.0 · before 11.5.211.5.2
Gogithub.com/mattermost/mattermost/server/v8before 8.0.0-20260313190740-742e0be950748.0.0-20260313190740-742e0be95074

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

Published before and after this one in the same product

  • ← EarlierCVE-2026-3495May 18, 2026 · Unescaped variables during error page composition
    19Monitor
  • ← EarlierCVE-2026-3637May 18, 2026 · Mattermost fails to enforce create_post permission when editing posts
    17Monitor
  • Later →CVE-2026-6334May 18, 2026 · OAuth authorization code client binding not enforced during token redemption in Mattermost
    15Monitor

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-server10.11.14+incompatiblePackage registry (OSV)
Go:github.com/mattermost/mattermost-server11.5.2+incompatiblePackage registry (OSV)
Go:github.com/mattermost/mattermost-server5.3.2-0.20260313190740-742e0be95074Package registry (OSV)
Go:github.com/mattermost/mattermost/server/v810.11.14Package registry (OSV)
Go:github.com/mattermost/mattermost/server/v811.5.2Package registry (OSV)
Go:github.com/mattermost/mattermost/server/v88.0.0-20260313190740-742e0be95074Package 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-2026-738725 days apartMattermost group syncable endpoints allow privilege escalation via scheme_admin
    35Monitor
  • CVE-2025-25274423 days apartUnauthorized Command Execution in Archived Channels
    35Monitor
  • CVE-2026-981691 days apartInsufficient server-side validation of board member role fields permits privilege escalation
    33Monitor
  • CVE-2026-673925 days apartMattermost: Delegated admins could patch protected default system roles
    28Monitor
  • CVE-2026-1010656 days apartUnauthorized users can trigger interactive post actions in private channels via action cookie channel mismatch in Mattermost
    26Monitor
  • CVE-2026-246263 days apartAdmin RCE via Malicious Plugin Upload on CI Test Instances
    26Monitor

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
low · data or configuration can be modified
Availability
none
Attack vector
Network
Attack complexity
Low
Privileges required
Low
User interaction
None
Scope
Unchanged
Confidentiality impact
None
Integrity impact
Low
Availability impact
None

Weakness class (CWE)

CWE-863 · Incorrect Authorization

CVSS vector

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

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.

MITRE has no CAPEC/ATT&CK mapping for this CWE.

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