CVE-2026-2458· NVD / CVE Program· CNA Mattermost

Unauthorized channel enumeration in private teams after member removal

Mattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 fail to properly validate team membership when searching channels which allows a removed team member to enumerate all public channels within a private team via the channel search API endpoint.. Mattermost Advisory ID: MMSA-2025-00568

MediumCVSS 4.3 · v3.1—No exploit Fix available

Broken access control (IDOR)

Published: Mar 16, 2026
Updated: Jun 17, 2026
EPSS: 0.2% · 5th percentile
CWE: CWE-862

Follow this CVE

Report tools

JSON

Action score

Monitor

Low priority for now.

CVSS: 17 / 40 · 4.3 / 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: —
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.

Affected systems

Vendor	Product	CPE
mattermost	mattermost server	cpe:2.3:a:mattermost:mattermost_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 10.11.11
mattermost mattermost server11.2.0 and later · before 11.2.3
mattermost mattermost server11.3.0 and later · before 11.3.1

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
- 11.4.0, 11.3.1, 11.2.3, 10.11.11not affected
- 11.3.0 and later · up to and including 11.3.0affected · semver
- 11.2.0 and later · up to and including 11.2.2affected · semver
- 10.11.0 and later · up to and including 10.11.10affected · semver

Package-level exposure

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

Ecosystem	Package	Affected range	Fix
Go	github.com/mattermost/mattermost-server	from 10.11.0-rc1 · before 10.11.11	10.11.11
Go	github.com/mattermost/mattermost-server	from 10.11.0-rc1+incompatible · before 10.11.11+incompatible	10.11.11+incompatible
Go	github.com/mattermost/mattermost-server	from 11.2.0-rc1 · before 11.2.3	11.2.3
Go	github.com/mattermost/mattermost-server	from 11.2.0-rc1+incompatible · before 11.2.3+incompatible	11.2.3+incompatible
Go	github.com/mattermost/mattermost-server	from 11.3.0-rc1 · before 11.3.1	11.3.1
Go	github.com/mattermost/mattermost-server	from 11.3.0-rc1+incompatible · before 11.3.1+incompatible	11.3.1+incompatible
Go	github.com/mattermost/mattermost-server	before 5.3.2-0.20260113182106-a18b80ba4c32	5.3.2-0.20260113182106-a18b80ba4c32
Go	github.com/mattermost/mattermost-server/v5	all versions	—
Go	github.com/mattermost/mattermost-server/v6	all versions	—
Go	github.com/mattermost/mattermost/server/v8	before 8.0.0-20260113182106-a18b80ba4c32	8.0.0-20260113182106-a18b80ba4c32
openSUSE:Leap 15.6	govulncheck-vulndb	before 0.0.20260326T203309-150000.1.155.2	0.0.20260326T203309-150000.1.155.2

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 / package	Fixed version	Source
Go:github.com/mattermost/mattermost-server	10.11.11	Package registry (OSV)
Go:github.com/mattermost/mattermost-server	10.11.11+incompatible	Package registry (OSV)
Go:github.com/mattermost/mattermost-server	11.2.3	Package registry (OSV)
Go:github.com/mattermost/mattermost-server	11.2.3+incompatible	Package registry (OSV)
Go:github.com/mattermost/mattermost-server	11.3.1	Package registry (OSV)
Go:github.com/mattermost/mattermost-server	11.3.1+incompatible	Package registry (OSV)
Go:github.com/mattermost/mattermost-server	5.3.2-0.20260113182106-a18b80ba4c32	Package registry (OSV)
Go:github.com/mattermost/mattermost/server/v8	8.0.0-20260113182106-a18b80ba4c32	Package registry (OSV)
opensuse:govulncheck-vulndb	0.0.20260326T203309-150000.1.155.2 · openSUSE:Leap 15.6	Package 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.

0x7oda7123finder

Variant candidates

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

CVE-2025-58073151 days apartArbitrary Mattermost Team can be joined by manipulating the OAuth state
32Monitor
CVE-2025-58075151 days apartArbitrary Mattermost Team can be joined by manipulating the SAML RelayState
32Monitor
CVE-2026-311763 days apartInstance and webhook GitLab plugin commands were able to be run by non-admin users
26Monitor
CVE-2026-516363 days apartMissing authorization check in AI message rewrite endpoint allows access to private thread content
26Monitor
CVE-2025-9076182 days apartMattermost Server exposes sensitive user credentials during shared channel membership synchronization
26Monitor
CVE-2026-513998 days apartGitLab Plugin Allows Non-Admin Users to Modify Default Instance Configuration
21Monitor

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

Mattermost Public Bug Bounty Engagement Bugcrowd · paid · up to $2,000

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: low · data can be read
Integrity: none
Availability: none

Attack vector: Network
Attack complexity: Low
Privileges required: Low
User interaction: None
Scope: Unchanged
Confidentiality impact: Low
Integrity impact: None
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:L/I:N/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.

Attack patterns (CAPEC)

Exploitation of Thunderbolt Protection FlawsCAPEC-665likelihood: Low · Very High

ATT&CK techniques

Noroxi analysis

No Noroxi analysis for this record yet

We don't hand-write analysis for all 385,000+ vulnerabilities; that wouldn't be honest. For notable, high-impact vulnerabilities our team writes the mechanism, detection and remediation steps.

We use this product, ask for help

Change log

Fix✗ → ✓Sep 28, 2026, 10:48 PM UTC

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

References

mattermost.com/security-updates

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

All records