NVD / CVE Program· CNA Mattermost

CVE-2026-4858: Path traversal in integration action URL leading to arbitrary API execution via system admin’s auth token.

Noroxi assessment

Priority: Monitor (action score 39/100)

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: 0.32% (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) 10.11.15, 10.11.15+incompatible, 11.4.5.

Low priority for now. Upgrade to github.com/mattermost/mattermost-server (Go) 10.11.15, 10.11.15+incompatible, 11.4.5 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 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to check integration URL for path traversal which allows an malicious authenticated user to call an arbitrary API via system admin Mattermost auth token using via path traversal in integration action URL.. Mattermost Advisory ID: MMSA-2026-00640

CriticalCVSS 9.9 · v3.1—No exploit Fix available

Path traversal

Published: May 21, 2026
Updated: Jul 23, 2026
EPSS: 0.3% · 25th percentile
CWE: CWE-22

Report tools

JSON

Action score

Monitor

Low priority for now.

CVSS: 39 / 40 · 9.9 / 10
CISA KEV: 0 / 30 · Not listed
EPSS: 0 / 30 · 0.3%

CISA SSVC decision

Exploitation: none
Automatable: no
Technical impact: total

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD: 9.9
CNA · Mattermost: 8.0; 1.9 point gap

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

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.

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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.

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 10.11.15
mattermost mattermost server11.4.0 and later · before 11.4.5
mattermost mattermost server11.5.0 and later · before 11.5.4
mattermost mattermost server11.6.0

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
- 11.7.0, 11.6.1, 11.5.4, 11.4.5, 10.11.15not affected
- 11.6.0 and later · up to and including 11.6.0affected · semver
- 11.5.0 and later · up to and including 11.5.3affected · semver
- 11.4.0 and later · up to and including 11.4.4affected · semver
- 10.11.0 and later · up to and including 10.11.14affected · 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 · before 10.11.15	10.11.15
Go	github.com/mattermost/mattermost-server	from 10.11.0+incompatible · before 10.11.15+incompatible	10.11.15+incompatible
Go	github.com/mattermost/mattermost-server	from 11.4.0 · before 11.4.5	11.4.5
Go	github.com/mattermost/mattermost-server	from 11.4.0+incompatible · before 11.4.5+incompatible	11.4.5+incompatible
Go	github.com/mattermost/mattermost-server	from 11.5.0 · before 11.5.4	11.5.4
Go	github.com/mattermost/mattermost-server	from 11.5.0+incompatible · before 11.5.4+incompatible	11.5.4+incompatible
Go	github.com/mattermost/mattermost-server	from 11.6.0 · before 11.6.1	11.6.1
Go	github.com/mattermost/mattermost-server	from 11.6.0+incompatible · before 11.6.1+incompatible	11.6.1+incompatible

Same product

mattermost: all records

Other highest-scoring records for the same primary product.

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

Published before and after this one in the same product

← EarlierCVE-2026-6347May 18, 2026 · Mattermost Calls plugin exposes TURN server credentials in plaintext in support packets
30Monitor
← EarlierCVE-2026-4055May 21, 2026 · Insufficient permission validation on cross-team playbook run creation
17Monitor
Later →CVE-2026-3473May 22, 2026 · Improper file ownership validation in the Boards API allows unauthorised file access
28Monitor

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	10.11.15	Package registry (OSV)
Go:github.com/mattermost/mattermost-server	10.11.15+incompatible	Package registry (OSV)
Go:github.com/mattermost/mattermost-server	11.4.5	Package registry (OSV)
Go:github.com/mattermost/mattermost-server	11.4.5+incompatible	Package registry (OSV)
Go:github.com/mattermost/mattermost-server	11.5.4	Package registry (OSV)
Go:github.com/mattermost/mattermost-server	11.5.4+incompatible	Package registry (OSV)
Go:github.com/mattermost/mattermost-server	11.6.1	Package registry (OSV)
Go:github.com/mattermost/mattermost-server	11.6.1+incompatible	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.

daw10finder

Variant candidates

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

CVE-2025-25279451 days apartArbitrary file read in Mattermost Boards via import & export board archive
37Monitor
CVE-2026-696122 days apartCVE-2026-6961: Path traversal via unsanitized FileInfo.Name in Mattermost federation sync
30Monitor
CVE-2025-9079244 days apartAdmin RCE via prepackaged plugins by way of misconfigured imports directory
28Monitor
CVE-2025-20051451 days apartArbitrary file read via block duplication in Mattermost Boards
26Monitor
CVE-2026-752168 days apartSAML certificate deletion allows path traversal to delete arbitrary files outside the config directory
22Monitor
CVE-2026-311256 days apartArbitrary File Read via Advanced Logging Support Packet
19Monitor

Chain candidates

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

CVE-2026-957153 days apartDeactivated user accounts can continue to obtain valid OAuth access tokens via refresh token grant in Mattermost
26Monitor
CVE-2026-667332 days apartMattermost Jira plugin had unauthenticated {{/ac/installed}} lifecycle callback during pending Jira Cloud install
25Monitor
CVE-2026-959753 days apartDeactivated guest accounts can authenticate via magic-link token in Mattermost REST API login endpoint
21Monitor
CVE-2026-63343 days apartOAuth authorization code client binding not enforced during token redemption in Mattermost
15Monitor

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: high · data can be read
Integrity: high · data or configuration can be modified
Availability: high · the service can be disrupted

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

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

Weakness class (CWE)

CWE-22 · Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')

CVSS vector

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

nvd-primary

Root cause

A user-supplied file name is joined with the allowed directory, but the result is never checked to confirm it is still inside that directory.

The bug in code

The whole CWE-22 class

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

Vulnerable

1const file = path.join(ROOT, req.query.name);
2res.sendFile(file);

Fixed

1const file = path.resolve(ROOT, req.query.name);
2if (!file.startsWith(ROOT + path.sep)) {
3  return res.sendStatus(400);
4}
5res.sendFile(file);

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

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Change log

Fix✗ → ✓Sep 28, 2026, 10:44 PM UTC

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References

mattermost.com/security-updates

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

All records