CVE-2026-6346· NVD / CVE Program· CNA Mattermost

Sensitive credentials exposed in plaintext in Mattermost support packets

Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13, 11.4.x <= 11.4.3 fail to sanitize sensitive configuration fields before including them in support packet generation, which allows a Mattermost System Admin or any party with access to a support packet to obtain sensitive credentials in plaintext via downloading a support packet from the System Console.. Mattermost Advisory ID: MMSA-2026-00607

HighCVSS 8.7 · v3.1—No exploit Fix available

Info leak

Published: May 18, 2026
Updated: Jun 17, 2026
EPSS: 0.4% · 33th percentile
CWE: CWE-200

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Action score

Monitor

Low priority for now.

CVSS: 34 / 40 · 8.7 / 10
CISA KEV: 0 / 30 · Not listed
EPSS: 0 / 30 · 0.4%

CISA SSVC decision

Exploitation: none
Automatable: no
Technical impact: total

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD: —
CNA · Mattermost: 8.7; 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.

Noroxi analysis

No Noroxi analysis for this record yet

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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 10.11.14
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.

Ecosystem	Package	Affected range	Fix
Go	github.com/mattermost/mattermost-server	from 10.11.0+incompatible · before 10.11.14+incompatible	10.11.14+incompatible
Go	github.com/mattermost/mattermost-server	from 11.4.0+incompatible · before 11.4.4+incompatible	11.4.4+incompatible
Go	github.com/mattermost/mattermost-server	from 11.5.0+incompatible · before 11.5.2+incompatible	11.5.2+incompatible
Go	github.com/mattermost/mattermost-server	before 5.3.2-0.20260326202606-fac92f4a71f3	5.3.2-0.20260326202606-fac92f4a71f3
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	from 10.11.0 · before 10.11.14	10.11.14
Go	github.com/mattermost/mattermost/server/v8	from 11.4.0 · before 11.4.4	11.4.4
Go	github.com/mattermost/mattermost/server/v8	from 11.5.0 · before 11.5.2	11.5.2
Go	github.com/mattermost/mattermost/server/v8	before 8.0.0-20260326202606-fac92f4a71f3	8.0.0-20260326202606-fac92f4a71f3

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	10.11.14+incompatible	Package registry (OSV)
Go:github.com/mattermost/mattermost-server	11.4.4+incompatible	Package registry (OSV)
Go:github.com/mattermost/mattermost-server	11.5.2+incompatible	Package registry (OSV)
Go:github.com/mattermost/mattermost-server	5.3.2-0.20260326202606-fac92f4a71f3	Package registry (OSV)
Go:github.com/mattermost/mattermost/server/v8	10.11.14	Package registry (OSV)
Go:github.com/mattermost/mattermost/server/v8	11.4.4	Package registry (OSV)
Go:github.com/mattermost/mattermost/server/v8	11.5.2	Package registry (OSV)
Go:github.com/mattermost/mattermost/server/v8	8.0.0-20260326202606-fac92f4a71f3	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.

Edgar Bellot Micófinder

Variant candidates

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

CVE-2026-63470 days apartMattermost Calls plugin exposes TURN server credentials in plaintext in support packets
30Monitor
CVE-2025-1382191 days apartUser profile update exposes password hash and MFA secrets
22Monitor
CVE-2026-604625 days apartPlugin bot username conflict allows user account to be used as bot identity in Mattermost Server
21Monitor
CVE-2025-11794185 days apartPassword hash and MFA secret returned in user email verification endpoint
19Monitor
CVE-2026-36364 days apartSanitize team member data returned by API
17Monitor
CVE-2026-343325 days apartMattermost fails to scope role_updated websocket events to authorized team and channel members
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

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.

National notice (Türkiye Cybersecurity Directorate / USOM)

Official security notices citing this record; remediation advice is on the agency's page.

TR-26-0272 · May 20, 2026(Mattermost Uygulama Güvenlik Bildirimi)

All national notices →

Technical details

Attack conditions

Anyone who can reach it over the internet can trigger it.
Administrator privileges are required.
No user action is required.
No special conditions are required; it is repeatable.

If successful

Confidentiality: high · data can be read
Integrity: high · data or configuration can be modified
Availability: none

Impact can extend beyond the vulnerable component (scope changes).

Attack vector: Network
Attack complexity: Low
Privileges required: High
User interaction: None
Scope: Changed
Confidentiality impact: High
Integrity impact: High
Availability impact: None

Weakness class (CWE)

CWE-200 · Exposure of Sensitive Information to an Unauthorized Actor

CVSS vector

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

nvd-secondary

Root cause

The extension requests broader permissions than its function needs and sends the data it collects out for purposes beyond its stated function.

The bug in code

The whole CWE-200 class

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

Vulnerable

json

1{2  "permissions": ["tabs", "<all_urls>"],3  "background": { "service_worker": "analytics.js" }4}

Fixed

json

1{2  "permissions": ["activeTab"],3  "host_permissions": ["https://yildiz.example/*"]4}

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)

ATT&CK techniques

Change log

Fix✗ → ✓Sep 28, 2026, 10:46 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

Noroxi analysis

No Noroxi analysis for this record yet

We use this product, ask for help

Data sources and verification

CNA: Mattermost

CVE.org (CNA)May 18, 2026, 2:37 PM UTC
CISA ADPMay 18, 2026, 2:37 PM UTC
NVDJun 17, 2026, 7:00 AM UTC
FIRST EPSSOct 4, 2026, 12:00 AM UTC
OSV / GHSAOct 5, 2026, 3:22 AM UTC

Each line is when that source was last processed for this record.

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