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NVD / CVE Program· CNA Mattermost

CVE-2026-3637: Mattermost fails to enforce create_post permission when editing posts

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: 0.15% (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, 11.4.4+incompatible, 11.5.2+incompatible; github.com/mattermost/mattermost/server/v8 (Go) 10.11.14, 11.4.4, 11.5.2.

Low priority for now. Upgrade to github.com/mattermost/mattermost-server (Go) 10.11.14+incompatible, 11.4.4+incompatible, 11.5.2+incompatible; github.com/mattermost/mattermost/server/v8 (Go) 10.11.14, 11.4.4, 11.5.2 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, 11.4.x <= 11.4.3 fail to check the create_post channel permission during post edit operations which allows an authenticated attacker with revoked posting privileges to modify their existing posts via direct API requests to the post update and patch endpoints.. Mattermost Advisory ID: MMSA-2026-00627

MediumCVSS 4.3 · v3.1—No exploit Fix available
Published
May 18, 2026
Updated
Oct 14, 2026
EPSS
0.1% · 4th 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
—
CNA · Mattermost
4.3
NVD has not scored this yet; the score shown is the CNA’s.

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-2026-3637

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 server11.4.0 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-serverfrom 10.11.0+incompatible · before 10.11.14+incompatible10.11.14+incompatible
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+incompatible · before 11.5.2+incompatible11.5.2+incompatible
Gogithub.com/mattermost/mattermost-serverbefore 5.3.2-0.20260316171743-090408f09f535.3.2-0.20260316171743-090408f09f53
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 11.4.0 · before 11.4.411.4.4
Gogithub.com/mattermost/mattermost/server/v8from 11.5.0 · before 11.5.211.5.2
Gogithub.com/mattermost/mattermost/server/v8before 8.0.0-20260316171743-090408f09f538.0.0-20260316171743-090408f09f53

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-2026-2325May 18, 2026 · Improper Input Validation in MS Teams Meetings API Handler
    26Monitor
  • ← EarlierCVE-2026-3495May 18, 2026 · Unescaped variables during error page composition
    19Monitor
  • Later →CVE-2026-4273May 18, 2026 · Insufficient token rotation validation in remote cluster invite confirmation
    17Monitor

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-server11.4.4+incompatiblePackage registry (OSV)
Go:github.com/mattermost/mattermost-server11.5.2+incompatiblePackage registry (OSV)
Go:github.com/mattermost/mattermost-server5.3.2-0.20260316171743-090408f09f53Package registry (OSV)
Go:github.com/mattermost/mattermost/server/v810.11.14Package registry (OSV)
Go:github.com/mattermost/mattermost/server/v811.4.4Package registry (OSV)
Go:github.com/mattermost/mattermost/server/v811.5.2Package registry (OSV)
Go:github.com/mattermost/mattermost/server/v88.0.0-20260316171743-090408f09f53Package 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.

No history yet (it accumulates with the daily EPSS job).

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-2025-58073214 days apartArbitrary Mattermost Team can be joined by manipulating the OAuth state
    32Monitor
  • CVE-2025-58075214 days apartArbitrary Mattermost Team can be joined by manipulating the SAML RelayState
    32Monitor
  • CVE-2026-8821119 days apartPlaybooks run owner channel membership permission bypass
    28Monitor
  • CVE-2026-31170 days apartInstance and webhook GitLab plugin commands were able to be run by non-admin users
    26Monitor
  • CVE-2026-51630 days apartMissing authorization check in AI message rewrite endpoint allows access to private thread content
    26Monitor
  • CVE-2025-9076245 days apartMattermost Server exposes sensitive user credentials during shared channel membership synchronization
    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-862 · Missing Authorization

CVSS vector

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

nvd-secondary

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